Method and apparatus for transmitting reference signal in mobile communication system

ABSTRACT

The present disclosure relates to a communication method and system for converging a 5th-Generation (5G) communication system for supporting higher data rates beyond a 4th-Generation (4G) system with a technology for Internet of Things (IoT). The present disclosure may be applied to intelligent services based on the 5G communication technology and the IoT-related technology, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services. A method by which a terminal receives a signal in a mobile communication system, according to one embodiment of the present specification, comprises the steps of: receiving channel state information-reference signal (CSI-RS) mode information; and receiving a signal on the basis of the CSI-RS mode information. Unlike a conventional method of allowing a base station to periodically set the CSI-RS in a terminal at a predetermined position such that the terminal receives the CSI-RS and generates and reports channel state information, the present invention proposes a method by which a base station allocates, to a terminal, a reference signal transmission for enabling aperiodic generation of the channel state information for a system having various numbers of transmission antenna ports such as one, two, four, eight, twelve, sixteen or thirty-two transmission antenna ports, and receives the channel state information report. In addition, a method for transferring ZP CSI-RS and quasi co-location (QCL) information for supporting rate matching thereby is also proposed.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation Application of Ser. No. 16/327,624filed on Feb. 22, 2019, which will be issued as U.S. Pat. No. 11,108,515on Aug. 31, 2021; which is a U.S. National Stage application under 35U.S.C. § 371 of an International application number PCT/KR2017/009269filed on Aug. 24, 2017; and was based on and claimed priority under 35U.S.C. § 119(a) of a Korean patent application number 10-2016-0107836,filed on Aug. 24, 2016, and of a Korean patent application number10-2016-0129970, filed on Oct. 7, 2016, in the Korean IntellectualProperty Office, the disclosure of each of which is incorporated byreference herein in its entirety.

TECHNICAL FIELD

The present invention relates to a method for transmitting and receivinga reference signal for signal transmission and reception in a mobilecommunication system and an apparatus using the method.

More particularly, the present invention relates a method for CSI-RStransmission and channel state feedback in a communication system, andan apparatus using the method.

BACKGROUND ART

To meet the demand for wireless data traffic having increased sincedeployment of 4G communication systems, efforts have been made todevelop an improved 5G or pre-5G communication system. Therefore, the 5Gor pre-5G communication system is also called a ‘Beyond 4G Network’ or a‘Post LTE System’. The 5G communication system is considered to beimplemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, soas to accomplish higher data rates. To decrease propagation loss of theradio waves and increase the transmission distance, the beamforming,massive multiple-input multiple-output (MIMO), Full Dimensional MIMO(FD-MIMO), array antenna, an analog beam forming, large scale antennatechniques are discussed in 5G communication systems. In addition, in 5Gcommunication systems, development for system network improvement isunder way based on advanced small cells, cloud Radio Access Networks(RANs), ultra-dense networks, device-to-device (D2D) communication,wireless backhaul, moving network, cooperative communication,Coordinated Multi-Points (CoMP), reception-end interference cancellationand the like. In the 5G system, Hybrid FSK and QAM Modulation (FQAM) andsliding window superposition coding (SWSC) as an advanced codingmodulation (ACM), and filter bank multi carrier (FBMC), non-orthogonalmultiple access (NOMA), and sparse code multiple access (SCMA) as anadvanced access technology have been developed.

The Internet, which is a human centered connectivity network wherehumans generate and consume information, is now evolving to the Internetof Things (IoT) where distributed entities, such as things, exchange andprocess information without human intervention. The Internet ofEverything (IoE), which is a combination of the IoT technology and theBig Data processing technology through connection with a cloud server,has emerged. As technology elements, such as “sensing technology”,“wired/wireless communication and network infrastructure”, “serviceinterface technology”, and “Security technology” have been demanded forIoT implementation, a sensor network, a Machine-to-Machine (M2M)communication, Machine Type Communication (MTC), and so forth have beenrecently researched. Such an IoT environment may provide intelligentInternet technology services that create a new value to human life bycollecting and analyzing data generated among connected things. IoT maybe applied to a variety of fields including smart home, smart building,smart city, smart car or connected cars, smart grid, health care, smartappliances and advanced medical services through convergence andcombination between existing Information Technology (IT) and variousindustrial applications.

In line with this, various attempts have been made to apply 5Gcommunication systems to IoT networks. For example, technologies such asa sensor network, Machine Type Communication (MTC), andMachine-to-Machine (M2M) communication may be implemented bybeamforming, MIMO, and array antennas. Application of a cloud RadioAccess Network (RAN) as the above-described Big Data processingtechnology may also be considered to be as an example of convergencebetween the 5G technology and the IoT technology.

The present invention provides a method and apparatus for a terminal tomeasure interference and generate channel state information in a mobilecommunication system where a base station (Evolved Node B, eNB) performsMIMO transmission using a plurality of transmit antennas.

In contrast to early mobile communication systems having providedvoice-oriented services only, to provide data services and multimediaservices, current mobile communication systems are evolving intohigh-speed and high-quality wireless packet data communication systems.Recently, various mobile communication standards, such as 3GPP highspeed downlink packet access (HSDPA), high speed uplink packet access(HSUPA), long term evolution (LTE), LTE-advanced (LTE-A), 3GPP2 highrate packet data (HRPD), and IEEE 802.16, have been developed to providehigh-speed and high-quality packet data services. In particular, the LTEsystem is developed to efficiently support high-speed wireless packetdata transmission and tries to maximize the wireless system capacity byutilizing various wireless access technologies. The LTE-A system is anadvanced version of the LTE system and supports improved datatransmission capabilities compared to the LTE system.

In general, LTE refers to the base station and terminal equipmentcorresponding to 3GPP Release 8 or 9, and LTE-A refers to the basestation and terminal equipment corresponding to 3GPP Release 10. In the3GPP standards body, even after standardization of the LTE-A system,standardization is being carried out for the subsequent systems withimproved performance.

The existing 3G and 4G wireless packet data communication systemsincluding HSDPA, HSUPA, HRPD, LTE, and LTE-A systems employ varioustechnologies such as adaptive modulation and coding (AMC) and channelsensitive scheduling in order to increase transmission efficiency. Byuse of AMC, the transmitter can adjust the amount of transmission dataaccording to the channel state. That is, when the channel state is notacceptable, the transmitter can reduce the amount of transmission dataso as to adjust the probability of a reception error to a desired level;and when the channel state is acceptable, the transmitter can increasethe amount of transmission data so as to effectively deliver a largeamount of information while adjusting the probability of a receptionerror to a desired level. By use of resource management based onchannel-sensitive scheduling, the transmitter may selectively provide aservice to a user with a good channel state among multiple users,increasing the system throughput in comparison to assigning a channel toone user and providing a service to the user. Such throughput incrementis referred to as multi-user diversity gain. Namely, AMC andchannel-sensitive scheduling are methods that enable the transmitter toapply an appropriate modulation and coding technique at the mostefficient point in time determined on the basis of partial channel stateinformation fed back from the receiver.

When AMC is used together with multiple input multiple output (MIMO)transmission, it may also determine the number of spatial layers (orrank) for the transmitted signal. In this case, to determine the optimaldata rate, AMC may consider not only the coding rate and modulationscheme but also the number of layers used for transmission using MIMO.

Recently, studies have been actively conducted to make a transition fromcode division multiple access (CDMA) being a multiple access scheme for2G and 3G mobile communication systems to orthogonal frequency divisionmultiple access (OFDMA) in the next generation system. 3GPP and 3GPP2have initiated standardization of evolutionary systems using OFDMA. Alarger capacity increase can be expected in the OFDMA scheme comparedwith the CDMA scheme. One of many causes of capacity increase in theOFDMA scheme is that it is possible to apply frequency domainscheduling. Just as a capacity gain is obtained throughchannel-sensitive scheduling according to the time-varying nature of thechannel, more capacity gain can be obtained if it is possible to utilizethe nature of the channel changing with frequency.

Accordingly, there is a need for a method and apparatus that performreference signal transmission and channel information feedback in acommunication system.

DISCLOSURE OF INVENTION Technical Problem

The CSI-RS overhead has increased in a mobile communication system owingto an increase in the number of antennas supported by the base stationand the necessity of per-terminal CSI-RS functionality to support theUE-specific beamformed CSI-RS technology. Hence, for efficient systemand CSI-RS operation management, there is a need for a method andapparatus that enable the base station to allocate an aperiodic CSI-RS(other than the existing periodic CSI-RS) to a terminal as necessary andenable the terminal to report channel state information based on theaperiodic CSI-RS.

Accordingly, the present invention proposes a method that enables thebase station to assign CSI-RS resource information in advance to theterminal and trigger it so as to allocate an aperiodic CSI-RS to theterminal. The aperiodic CSI-RS can be configured based on the CSI-RS REsupported by the existing Release 13 specification. Alternatively, onlythe CSI-RS can be transmitted in a specific subframe, subband or RBwithout PDSCH transmission. In the first option, a CSI-RS pool may beformed based on a plurality of existing CSI-RS settings, and the basestation can allocate a CSI-RS aperiodically. In the second option, thePDSCH is not transmitted in the corresponding RB and a DMRS for PDSCHdecoding is not required correspondingly. As this resource is allocateddynamically based on the PCFICH, the amount of resources may varydepending on the situation, and thus the port indexing must also bechanged. The present invention proposes a method and apparatus forhandling configurations, allocations, and procedures related toaperiodic CSI-RS transmission.

Solution to Problem

In accordance with an aspect of the present invention, there is provideda method for a terminal to receive signals in a mobile communicationsystem. The method may include: receiving channel stateinformation-reference signal (CSI-RS) mode information; and receiving asignal based on the CSI-RS mode information.

In accordance with another aspect of the present invention, there isprovided a method for a base station to transmit signals in a mobilecommunication system. The method may include: transmitting channel stateinformation-reference signal (CSI-RS) mode information; and transmittinga signal based on the CSI-RS mode information.

In accordance with another aspect of the present invention, there isprovided a terminal in a mobile communication system. The terminal mayinclude: a transceiver configured to transmit and receive a signal; anda controller associated with the transceiver and configured to receivechannel state information-reference signal (CSI-RS) mode information andto receive a signal based on the CSI-RS mode information.

In accordance with another aspect of the present invention, there isprovided a base station in a mobile communication system. The basestation may include: a transceiver configured to transmit and receive asignal; and a controller associated with the transceiver and configuredto transmit channel state information-reference signal (CSI-RS) modeinformation and to transmit a signal based on the CSI-RS modeinformation.

Advantageous Effects of Invention

In a feature of the present invention, for semi closed-loop MIMOtransmission, precoder cycling can be applied within one RE based on theDMRS. In this case, a plurality of RBs can be transmitted as a bundle tosupport eight or more precoders. In addition, it is possible to performtransmission through multiple layers and terminals by use of the offset.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates time and frequency resources in the LTE system.

FIG. 2 depicts CSI-RS transmissions with 2, 4, and 8 antenna ports inthe LTE system.

FIG. 3 depicts a communication system to which the present invention isapplied.

FIG. 4 illustrates subframes and RBs for CSI-RS transmission proposed inthe present invention.

FIG. 5 depicts operations of the terminal to periodically report thechannel state using a bandwidth part in the LTE system.

FIG. 6 depicts resource allocation for PDSCH transmission throughdownlink resource allocation type 0 in the LTE system.

FIG. 7 depicts resource allocation for PDSCH transmission throughdownlink resource allocation type 1 in the LTE system.

FIG. 8 depicts resource allocation for PDSCH transmission throughdownlink resource allocation type 2 in the LTE system.

FIG. 9 depicts a situation where the aperiodic CSI-RS RB or subframeproposed in the present invention operates together with the existingperiodic CSI-RS.

FIG. 10 shows an example in which the aperiodic CSI-RS RB or subframeproposed in the present invention defines port indexes based on allavailable resources.

FIG. 11 shows an example in which the aperiodic CSI-RS RB or subframeproposed in the present invention divides all available resources intoexisting CSI-RS resources and new CSI-RS resources and defines portindexes separately.

FIG. 12 depicts a situation where the ZP CSI-RS proposed in the presentinvention is configured in advance and the aperiodic CSI-RS istransmitted to each ZP CSI-RS terminal.

FIG. 13 is a flowchart illustrating operations of the terminal accordingto an embodiment of the present invention.

FIG. 14 is a flowchart illustrating operations of the base stationaccording to an embodiment of the present invention.

FIG. 15 is a block diagram of a terminal according to an embodiment ofthe present invention.

FIG. 16 is a block diagram of a base station according to an embodimentof the present invention.

MODE FOR THE INVENTION

Hereinafter, embodiments of the present invention are described indetail with reference to the accompanying drawings. Descriptions ofwell-known functions and structures incorporated herein may be omittedto avoid obscuring the subject matter of the present invention. Theterms described below are defined in consideration of their functions inthe present invention, and these may vary depending on the intention ofthe user, the operator, or the custom. Hence, their meanings should bedetermined based on the overall contents of this specification.

The aspects, features, and advantages of certain embodiments of thepresent invention will be more apparent from the following detaileddescription taken in conjunction with the accompanying drawings. Thedescription of the various embodiments does not describe every possibleinstance of the present invention. It should be apparent to thoseskilled in the art that the following description is provided forillustrative purposes only and not for the purpose of limiting thepresent invention as defined by the appended claims and theirequivalents. The same reference symbols are used throughout thedescription to refer to the same parts.

Meanwhile, it is known to those skilled in the art that blocks of aflowchart (or sequence diagram) and a combination of flowcharts may berepresented and executed by computer program instructions. Thesecomputer program instructions may be loaded on a processor of a generalpurpose computer, special purpose computer, or programmable dataprocessing equipment. When the loaded program instructions are executedby the processor, they create a means for carrying out functionsdescribed in the flowchart. As the computer program instructions may bestored in a computer readable memory that is usable in a specializedcomputer or a programmable data processing equipment, it is alsopossible to create articles of manufacture that carry out functionsdescribed in the flowchart. As the computer program instructions may beloaded on a computer or a programmable data processing equipment, whenexecuted as processes, they may carry out steps of functions describedin the flowchart.

A block of a flowchart may correspond to a module, a segment or a codecontaining one or more executable instructions implementing one or morelogical functions, or to a part thereof. In some cases, functionsdescribed by blocks may be executed in an order different from thelisted order. For example, two blocks listed in sequence may be executedat the same time or executed in reverse order.

In the description, the word “unit”, “module”, or the like may refer toa software component or hardware component such as an FPGA or ASICcapable of carrying out a function or an operation. However, “unit” orthe like is not limited to hardware or software. A unit or the like maybe configured so as to reside in an addressable storage medium or todrive one or more processors. Units or the like may refer to softwarecomponents, obj ect-oriented software components, class components, taskcomponents, processes, functions, attributes, procedures, subroutines,program code segments, drivers, firmware, microcode, circuits, data,databases, data structures, tables, arrays, or variables. A functionprovided by a component and unit may be a combination of smallercomponents and units, and it may be combined with others to composelarge components and units. Components and units may be configured todrive a device or one or more processors in a secure multimedia card.

Descriptions of well-known functions and structures incorporated hereinmay be omitted to avoid obscuring the subject matter of the presentinvention. Particular terms may be defined to describe the invention inthe best manner. Hence, the meaning of specific terms or words used inthe specification and the claims should be construed in accordance withthe spirit of the present invention.

The CSI-RS overhead has increased in a mobile communication system owingto an increase in the number of antennas supported by the base stationfor FD-MIMO and the necessity of per-terminal CSI-RS functionality tosupport the UE-specific beamformed CSI-RS technology. Hence, forefficient system and CSI-RS operation management, there is a need for amethod that enables the base station to allocate an aperiodic CSI-RS(other than the existing periodic CSI-RS) to a terminal as necessary andenables the terminal to report channel state information based on theaperiodic CSI-RS.

In the following description, LTE (long term evolution) and LTE-A(LTE-Advanced) systems are taken as an example for describing thepresent invention. However, the present invention is applicable to othercommunication systems using licensed and unlicensed bands withoutsignificant modification.

Next, a description is given of a method for configuring a plurality ofCSI-RS ports in consideration of one or more of the items describedabove.

FIG. 1 illustrates time and frequency resources in the LTE/LTE-A system.

With reference to FIG. 1, the radio resources transmitted from the basestation (eNB) to the terminal (user equipment (UE)) are divided intoresource blocks (RBs) in the frequency domain and are divided intosubframes in the time domain. In the LTE/LTE-A system, each RB generallyincludes twelve subcarriers and occupies a band of 180 kHz. In theLTE/LTE-A system, a subframe is generally composed of 14 OFDM symbolsand occupies a time duration of 1 msec. For scheduling, the LTE/LTE-Asystem can allocate resources in units of subframes in the time domainand allocate resources in units of RBs in the frequency domain.

FIG. 2 depicts CSI-RS transmissions with 2, 4, and 8 antenna ports usingradio resources of 1 subframe and 1 RB which are the minimum unit fordownlink scheduling in the LTE/LTE-A system.

In FIG. 2, the illustrated radio resources are composed of one subframein the time domain and one RB in the frequency domain. Such radioresources are composed of 12 subcarriers in the frequency domain and 14OFDM symbols in the time domain, thereby providing a total of 168frequency-time positions. In LTE/LTE-A, each frequency-time position inFIG. 2 is referred to as a resource element (RE).

The radio resources shown in FIG. 2 can be used to transmit thefollowing different types of signals.

1. CRS (cell specific reference signal): this is a reference signaltransmitted for all terminals in one cell

2. DMRS (demodulation reference signal): this is a reference signaltransmitted for a specific terminal and is used to perform channelestimation to recover information carried by the PDSCH. One DMRS port istransmitted with the same precoding as the PDSCH layer associatedtherewith. The terminal wishing to receive a specific layer of the PDSCHmay receive the DMRS port associated with the layer and perform channelestimation to restore information carried by the layer.

3. PDSCH (physical downlink shared channel): this is a data channeltransmitted in the downlink, and is used by the base station to transmittraffic to the terminal. The PDSCH is transmitted by using an RE throughwhich a reference signal is not transmitted in the data region of FIG.2.

4. CSI-RS (channel status information reference signal): this is areference signal transmitted for terminals belonging to one cell and isused for channel state measurement. A plurality of CSI-RSs may betransmitted in one cell.

5. ZP CSI-RS (zero power CSI-RS): this indicates that the actual signalis not transmitted at the position where the CSI-RS is transmitted.

6. IMR (interference measurement resource): this corresponds to aposition where the CSI-RS is transmitted, and one or more of thepositions labelled A, B, C, D, E, F, G, H, I and J in FIG. 2 can be setas an IMR. The terminal can perform interference measurement under anagreement that all signals received at the REs set as an IMR areinterference.

7. Other control channels (physical hybrid-ARQ indicator channel(PHICH), physical control format indicator channel (PCFICH), physicaldownlink control channel (PDCCH)): These control channels are used toprovide control information required by the terminal to receive thePDSCH or used to transmit ACK/NACK information for operating HARQ withrespect to an uplink data transmission.

In addition to the signals described above, the LTE-A system mayconfigure a zero power CSI-RS so that a CSI-RS from another base stationcan be received by terminals of the corresponding cell withoutinterference. The zero power CSI-RS (muting) may be applied to aposition where a CSI-RS can be transmitted, and the terminal receives atraffic signal normally by skipping the corresponding radio resource. Inthe LTE-A system, the zero power CSI-RS is also referred to as muting.This is because muting is applied to the CSI-RS position andtransmission power is not transmitted due to the characteristic ofmuting.

In FIG. 2, the CSI-RS may be transmitted using at least some of thepositions labelled A, B, C, D, E, F, G, H, I and J according to thenumber of antennas for CSI-RS transmission. Muting may also be appliedto some of the positions labelled A, B, C, D, E, F, G, H, I and J. Inparticular, the CSI-RS may be transmitted via two, four or eight REsdepending on the number of antenna ports for CSI-RS transmission. InFIG. 2, when the number of antenna ports is two, the CSI-RS istransmitted through a half of a specific pattern; when the number ofantenna ports is four, the CSI-RS is transmitted through the whole of aspecific pattern; and when the number of antenna ports is eight, theCSI-RS is transmitted using two patterns. In contrast, muting is alwaysapplied on a pattern basis. That is, muting may be applied to multiplepatterns, but cannot be applied to only a part of one pattern unless themuted position overlaps a CSI-RS position. Muting may be applied to apart of one pattern only when the muted position overlaps a CSI-RSposition.

When the CSI-RS is transmitted for 2 antenna ports, CSI-RSs for the twoantenna ports are transmitted through two REs adjacent in the timedomain and the signals of the individual antenna ports are separated byusing orthogonal codes. When the CSI-RS is transmitted for 4 antennaports, CSI-RSs for two antenna ports are transmitted through two REs inthe same way as above and CSI-RSs for the remaining two antenna portsare transmitted through additional two REs in the same way. The sameprocess may be applied to the case where the CSI-RS is transmitted for 8antennas ports.

The base station may boost the transmission power of the CSI-RS toimprove channel estimation accuracy. When the CSI-RS is transmitted forfour or eight antenna ports (AP), a particular CSI-RS port istransmitted only via a CSI-RS RE at a specified position and is nottransmitted via a different OFDM symbol in the same OFDM symbol group.

In addition, the terminal may be allocated a CSI-IM (or IMR(interference measurement resource)) together with a CSI-RS. The CSI-IMresource has the same configuration and position as the CSI-RSsupporting 4 ports. The CSI-IM is a resource used by a terminal thatreceives data from one or more base stations to accurately measure theinterference from a neighboring base station. For example, to measurethe amount of interference when a neighboring base station transmitsdata and the amount of interference when the neighboring base stationdoes not transmit data, the base station may configure the CSI-RS andtwo CSI-IM resources, and it may cause one CSI-IM resource to alwaystransmit the signal from the neighbor base station and cause the otherCSI-IM resource not to transmit the signal from the neighbor basestation. Thereby, the amount of interference from the neighboring basestation can be effectively measured.

In the LTE-A system, the base station can notify the terminal of CSI-RSconfiguration information through higher layer signaling. The CSI-RSconfiguration may include the index of the CSI-RS configuration, thenumber of ports included in the CSI-RS, the transmission period of theCSI-RS, the transmission offset, CSI-RS resource configurationinformation, CSI-RS scrambling ID, QCL information, and the like.

In FIG. 2, two options may be used for CSI-RS transmission according tothe number of CSI-RSs to be transmitted. To transmit 8 CSI-RSs or less(i.e., 1, 2, 4, or 8 CSI-RSs), the CSI-RS may be transmitted using someof the positions labelled A, B, C, D, E, F, G, H, I and J in FIG. 2according to the number of antennas for CSI-RS transmission. The zeropower CSI-RS (muting) may also be applied to some of the positionslabelled A, B, C, D, E, F, G, H, I and J. In particular, the CSI-RS maybe transmitted via two, four or eight REs depending on the number ofantenna ports. In FIG. 2, when the number of antenna ports is two, theCSI-RS is transmitted through a half of a specific pattern; when thenumber of antenna ports is four, the CSI-RS is transmitted through thewhole of a specific pattern; and when the number of antenna ports iseight, the CSI-RS is transmitted using two patterns. In contrast, thezero power CSI-RS (muting) is always applied on a pattern basis. Thatis, muting may be applied to multiple patterns, but cannot be applied toonly a part of one pattern unless the muted position overlaps a CSI-RSposition. Muting may be applied to a part of one pattern only when themuted position overlaps a CSI-RS position.

When the CSI-RS is transmitted for 2 antenna ports, signals for the twoantenna ports are respectively transmitted through two REs adjacent inthe time domain and the signals of the individual antenna ports are codedivision multiplexed (CDM) using orthogonal codes. When the CSI-RS istransmitted for 4 antenna ports, signals for two antenna ports arerespectively transmitted through two REs in the same way as above andsignals for the remaining two antenna ports are respectively transmittedthrough additional two REs in the same way. The same process may beapplied to the case where the CSI-RS is transmitted for 8 antennasports.

To transmit 12 or 16 CSI-RSs being more than 8 CSI-RSs, the existing 4or 8 CSI-RS positions are combined through RRC settings to transmit 12or 16 CSI-RSs. In other words, to transmit 12 CSI-RSs, three 4-portCSI-RS positions are bundled and transmitted as one 12-port CSI-RS. Totransmit 16 CSI-RSs, two 8-port CSI-RS positions are bundled andtransmitted as one 16-port CSI-RS. Unlike the existing 8 port or lessCSI-RS transmission, 12 and 16-port CSI-RS transmission supports CDM ofsize 4. The existing 8 port or less CSI-RS supports CDM2, and it cansupport power boosting up to 6 dB with respect to 8 ports by overlappingCSI-RS 2 ports with 2 time symbols, achieving full power utilization forCSI-RS transmission. However, in the case of 12-port or 16-port CSI-RS,full power utilization for CSI-RS transmission cannot be achieved withthe combination of CDM2 and 6 dB. In such a case, CDM4 helps to achievefull power utilization.

In a cellular system, the base station has to transmit a referencesignal to the terminal to measure the downlink channel state. In the3GPP LTE-A system, the terminal measures the channel state between thebase station and the terminal by using the CRS or CSI-RS transmittedfrom the base station. Channel state measurement basically involvesseveral factors including the amount of interference in the downlink.The amount of interference in the downlink includes an interferencesignal and thermal noise generated by antennas belonging to aneighboring base station, and it is important for the terminal todetermine the channel condition in the downlink. For example, when abase station having one transmit antenna transmits a signal a terminalhaving one receive antenna, by using a reference signal received fromthe base station, the terminal determines the energy per symbolreceivable in the downlink and the amount of interference to be receivedsimultaneously in the interval where the corresponding symbol isreceived, and calculates the value of Es/Io (energy per symbol tointerference density ratio). The determined value of Es/Io is convertedinto a value indicating the data transmission rate or a correspondingvalue, and is notified to the base station in the form of a channelquality indicator (CQI), enabling the base station to determine anappropriate data transmission rate for the terminal in the downlink.

In the LTE-A system, the terminal feeds back information on the downlinkchannel state to the base station, so that the base station may utilizethe feedback information for downlink scheduling. That is, the terminalmeasures a downlink reference signal sent by the base station and feedsback information extracted from the measurement to the base stationaccording to a rule specified in the LTE/LTE-A standard. In LTE/LTE-A,the terminal generally feeds back the following three pieces ofinformation.

1. Rank Indicator (RI): number of spatial layers available to theterminal in the current channel condition

2. Precoder Matrix Indicator (PMI): index to the precoding matrixpreferred by the terminal in the current channel condition

3. Channel Quality Indicator (CQI): maximum data rate available to theterminal in the current channel condition. The CQI may be replaced witha parameter similar to the maximum data rate, such as SINR, maximumerror correction coding rate associated with the modulation scheme, ordata efficiency per frequency.

The RI, PMI and CQI are associated with each other in meaning. Forexample, the precoding matrixes supported in LTE/LTE-A are defineddifferently for different ranks. Hence, the interpretation of the samePMI value when the RI is set to 1 is different from that when the RI isset to 2. In addition, when determining the CQI, the terminal assumesthat the PMI and RI values having been reported to the base station areapplied at the base station. For example, if the terminal has reportedRI_X, PMI_Y and CQI_Z to the base station, this means that the terminalis capable of receiving data at a data rate corresponding to CQI_Z onthe assumption of rank RI_X and precoding PMI_Y. In this way, theterminal may assume a transmission mode to be used by the base stationto calculate the CQI, so that optimal performance can be obtained whenactual transmission is performed according to the assumed transmissionmode.

For channel information generation and reporting, the base stationhaving a large number of antennas has to configure reference signalresources for measuring channels of eight or more antennas and transmitthem to the terminal. As shown in FIG. 2, the available CSI-RS resourcescan use up to 48 REs, but it is possible to configure up to 8 CSI-RSsper one CSI process at present. Therefore, a new CSI-RS configurationscheme is needed to support the FD-MIMO system that can operate based oneight or more CSI-RS ports. For example, in LTE/LTE-A Release 13, one,two, four, eight, twelve or sixteen CSI-RS ports can be configured forone CSI process. Specifically, for {1, 2, 4, 8} port CSI-RS, theexisting mapping rule is used. The 12-port CSI-RS is configured with acombination or aggregation of three 4-port CSI-RS patterns, and the16-port CSI-RS is configured with a combination of two 8-port CSI-RSpatterns. In LTE/LTE-A Release 13, for the 12 or 16-port CSI-RS, CDM-2or CDM-4 is supported using orthogonal cover codes (OCCs) of length 2 or4. The description of FIG. 3 is for CSI-RS power boosting based onCDM-2. According to the above description, a power boost of up to 9 dBwith respect to the PDSCH is required for full power utilization of the12 or 16-port CSI-RS based on CDM-2. This means that higher performancehardware is needed for full power utilization when operating the 12 or16-port CSI-RS based on CDM-2. Considering this fact, release 13 hasintroduced the 12 or 16-port CSI-RS based on CDM-4. Thereby, full powerutilization becomes possible with the same 6 dB power boost as before.

FIG. 3 depicts a communication system to which the present invention isapplied.

With reference to FIG. 3, the transmission equipment of the base stationtransmit radio signals by using dozens or more transmit antennas. Theplurality of transmit antennas are arranged so as to maintain a givenspace therebetween as shown in FIG. 3. The given space may correspondto, for example, a multiple of half the wavelength of a transmittedradio signal. Generally, when a space of half the wavelength of a radiosignal is maintained between transmit antennas, signals transmitted fromthe individual transmit antennas are influenced by radio channels havinglow correlation with each other. As the space between the transmitantennas increases, the correlation between the signals decreases.

In the base station equipment having a large number of antennas, theantennas can be arranged two-dimensionally as shown in FIG. 3 to preventthe equipment from becoming too large. In this case, the base stationtransmits a signal by using N_(H) antennas arranged on the horizontalaxis and N_(V) antennas arranged on the vertical axis, and the terminalhas to measure the channel for the corresponding antenna.

In FIG. 3, the dozens or more transmit antennas installed in thetransmission equipment of the base station are utilized to transmitsignals to one or more terminals. Appropriate precoding is applied to aplurality of transmit antennas to simultaneously transmit signals to aplurality of terminals. Here, one terminal may receive one or moreinformation streams. In general, the number of information streams thatone terminal can receive is determined according to the number ofreceive antennas of the terminal and the channel condition.

To effectively implement the MIMO system, as described above, theterminal must accurately measure channel conditions and interferencemagnitudes and transmit effective channel state information to the basestation based on the measurement data. Upon receiving the channel stateinformation, the base station determines a terminal to which data is tobe transmitted, a data transmission rate, precoding to be applied, andthe like with respect to downlink transmission. In case of the FD-MIMOsystem, the number of transmit antennas is large. Hence, when theexisting scheme of the LTE/LTE-A system is applied to transmit andreceive channel state information, an uplink overhead problem may occurthat requires transmission of a lot of control information in theuplink.

In a mobile communication system, time, frequency, and power resourcesare limited. If more resources are allocated to the reference signal,the resources that can be allocated to the transmission of the trafficchannel (data) are reduced and the amount of data actually transmittedcan be reduced. In such a case, although performance of channelmeasurement and estimation may be improved, the amount of actuallytransmitted data is reduced, so that the overall system capacityperformance may be lowered.

Therefore, a proper distribution is required between the resources forthe reference signal and the resources for the traffic channeltransmission to achieve optimum performance in terms of the overallsystem capacity.

The base station having a large number of antennas as shown in FIG. 3has to configure reference signal resources for measuring channels ofeight or more antennas and transmit them to the terminal. The availableresources can use up to 40 REs in FIG. 2, but in fact only 2, 4, and 8resources are available to one cell. Hence, to support channelmeasurement for a large number of antennas required in the FD-MIMOsystem, it is necessary to provide CSI-RS patterns for 16 or 32resources, which are not supported by the current system. For accurateand efficient CSI generation, these patterns should be designed inconsideration of various aspects such as power boosting and radiochannel estimator implementation.

Additionally, in a base station using conventional four horizontaldimension antennas, when vertical dimension antennas are used to improveperformance, the applicable size of antennas may not be four or eight.Hence, it is necessary to newly design CSI-RS patterns for supporting 12antennas and various other numbers of antennas with three verticalantennas.

Table 1 below shows RRC fields constituting the CSI-RS configuration.

TABLE 1 CSI-RS config CSI-IM config CQI report config Etc No. antennaports Resource config Periodic P 

  Resource config Time and frequency Mode, resource, Codebook subsetTime and frequency position in a subframe periodicity, offset..restriction position in a subframe Subframe config Aperiodic Subframeconfig Periodicity and subframe Mode.. Periodicity and subframe offsetPMI/RI report offset RI reference CSI Qcl-CRS-info (QCL process Type B)SubframePattern CRS Information for CoMP

indicates data missing or illegible when filed

The settings for reporting the channel state based on the periodicCSI-RS in the CSI process can be classified into four types as shown inTable 1. CSI-RS config is for setting the frequency and time position ofa CSI-RS RE. Here, the number-of-antennas setting indicates how manyports the corresponding CSI-RS has. Resource config specifies theposition of an RE in the RB, and Subframe config sets the period andoffset of the subframe. Tables 2 and 3 are for Resource config andSubframe config currently supported by LTE.

TABLE 2 CSI Reference Number of CSI reference signals configured signal1 or 2 4 8 configuration (k′, 1′) n_(s) mod 2 (k′, 1′) n_(s) mod 2 (k′,1′) n_(s) mod 2 Frame structure 0 (9, 5) 0 (9, 5) 0 (9, 5) 0 type 1 and2 1 (11, 2) 1 (11, 2) 1 (11, 2) 1 2 (9, 2) 1 (9, 2) 1 (9, 2) 1 3 (7, 2)1 (7, 2) 1 (7, 2) 1 4 (9, 5) 1 (9, 5) 1 (9, 5) 1 5 (8, 5) 0 (8, 5) 0 6(10, 2) 1 (10, 2) 1 7 (8, 2) 1 (8, 2) 1 8 (6, 2) 1 (6, 2) 1 9 (8, 5) 1(8, 5) 1 10 (3, 5) 0 11 (2, 5) 0 12 (5, 2) 1 13 (4, 2) 1 14 (3, 2) 1 15(2, 2) 1 16 (1, 2) 1 17 (0, 2) 1 18 (3, 5) 1 19 (2, 5) 1 Frame 20(11, 1) 1 (11, 1) 1 (11, 1) 1 structure type2 only 21 (9, 1) 1 (9, 1) 1(9, 1) 1 22 (7, 1) 1 (7, 1) 1 (7, 1) 1 23 (10, 1) 1 (10, 1) 1 24 (8, 1)1 (8, 1) 1 25 (6, 1) 1 (6, 1) 1 26 (5, 1) 1 27 (4, 1) 1 28 (3, 1) 1 29(2, 1) 1 30 (1, 1) 1 31 (0, 1) 1

Resource Config

TABLE 3 CSI-RS CSI-RS periodicity CSI-RS subframe offset Subframe configI_(CSI)_RS T_(CSI-RS) (subframes) Δ_(CSI-RS) (subframes) 0-4 5I_(CSI-RS)  5-14 10 I_(CSI-RS)-5  15-34 20 I_(CSI-RS)-15 35-74 40I_(CSI-RS)-35  75-154 80 I_(CSI-RS)-75

Subframe Config

The terminal can identify the frequency and time position, period andoffset from Tables 2 and 3 above. Qcl-CRS-info sets quasi co-locationinformation for CoMP. CSI-IM config is for setting the frequency andtime position of the CSI-IM for measuring interference. As the CSI-IM isalways set on a basis of four ports, it is not necessary to set thenumber of antenna ports, and Resource config and Subframe config are setin the same manner as the CSI-RS. CQI report config is to specify how toreport the channel state via the corresponding CSI process. CQI reportconfig may include settings regarding periodic channel status reporting,aperiodic channel status reporting, PMI/RI reporting, RI reference CSIprocess, and subframe patterns. In addition, there are a value of P_(C)indicating the power ratio between the PDSCH and the CSI-RS RE requiredfor the terminal to generate a channel status report, and Codebooksubset restriction indicating the codebook to be used.

In the case of an FD-MIMO base station, as described above, a referencesignal resource for measuring eight or more antenna channels must beconfigured and transmitted to the terminal. Here, the number ofreference signals may be determined according to the base stationantenna configuration and measurement type. For example, in LTE/LTE-ARelease 13, it is possible to configure {1, 2, 4, 8, 12, 16}-port CSI-RSon the assumption of full port mapping. Here, full port mapping meansthat all transceiver units (TXRU) have a dedicated CSI-RS port forchannel estimation.

Meanwhile, as described above, there is a high possibility that 16 ormore TXRUs will be introduced after LTE/LTE-A Release 14. Also, thenumber of available antenna array geometries will increase significantlycompared with Release 13. This means that LTE/LTE-A Release 14 shouldsupport a variable number of TXRUs. Table 4 shows availabletwo-dimensional antenna array geometries according to the number ofCSI-RS ports under full port mapping. In Table 4, {18, 20, 22, 24, 26,28, 30, 32}-port CSI-RSs are considered. Considering that two differentpolarized antennas may exist at the same position in a polarized antennaconfiguration, {9, 10, 11, 12, 13, 14, 15, 16} different AP positionscan be considered. The geometry of a two-dimensional rectangular orsquare antenna array can be represented by the number N₁ of different APpositions in the first dimension (vertical or horizontal) and the numberN₂ of different AP positions in the second dimension (horizontal orvertical), and possible combinations of the two port numbers are shownby (N₁, N₂) in Table 4. Table 4 shows that various antenna arraygeometries may exist depending on the number of CSI-RS ports.

TABLE 4 Number of Number of Available 2D antenna array Impact onaggregated aggregated CSI-RS geometry, (N₁, N₂) 2D RS and CSI-RS portsports per polarization (1D configurations were omitted) feedback design18 9 (3, 3) — — — Low 20 10 (2, 5) (5, 2) — — Med 22 11 — — — — — 24 12(2, 6) (3.4) (4, 3) (6, 2) High 26 13 — — — — — 28 14 (2, 7) (7, 2) — —Med 30 15 (3, 5) (5, 3) — — Med 32 16 (2, 8) (4, 4) (8, 2) — High

Available 2D antenna array geometry according to the number ofaggregated CSI-RS ports based on full port mapping

In order to support 16 or more CSI-RS ports as described above, it isnecessary to consider the following issues.

1. CSI-RS configurations with a large number of ports suitable forvarious 2-dimensional antenna array geometries including crosspolarization and various channel conditions

2. Reduction of CSI-RS resource overhead due to a large number of CSI-RSports

First Embodiment

There are two options for defining CSI-RS resources in one RB foraperiodic CSI-RS transmission.

1. Option 1 for defining time/frequency resources required for aperiodicCSI-RS transmission: transmission using existing CSI-RS REs.

2. Option 2 for defining time/frequency resources required for aperiodicCSI-RS: defining new resources for CSI-RS transmission.

Option 1 is to transmit the aperiodic CSI-RS through existing resourcesfor 1, 2, 4, 8-port CSI-RS transmission shown in FIG. 2. The advantageof this option is that it can transmit the PDSCH for data transmissiontogether with a new aperiodic CSI-RS to conventional and new terminals.However, in this option, when the base station allocates and transmitsaperiodic CSI-RS resources to a specific terminal, other terminalsreceiving data must be allocated the corresponding resources as a ZPCSI-RS.

Option 2 is to define new resources for CSI-RS transmission only.

FIG. 4 shows an example of a new resource region for CSI-RS transmissiononly.

With reference to FIG. 4, the full band, subband or RB corresponding toa particular subframe is used only for CSI-RS transmission. Here, theDMRS for PDSCH decoding need not be transmitted. Hence, the full bandexcept for the PDCCH transmission region and the CRS transmission regioncan be used as CSI-RS REs. In the case where the subframe in which theaperiodic CSI-RS transmission is configured is the MBSFN subframe, asthe CRS is transmitted only via the symbol where the PDCCH is to betransmitted, the number of CSI-RS REs can be further increased. In thecase of the special subframe, the subframe excluding the guard period(GP) and the uplink transmission interval (UpPTS) can be used. Forexample, assuming two PDCCH symbol transmission and MBSFN subframe, 144REs can be used for CSI-RS transmission. In this option, it is possibleto secure a large number of CSI-RS REs in one RB, thereby enablingsimultaneous transmissions to multiple terminals. Further, as the PDSCHis not transmitted, there is no need to separately configure the ZPCSI-RS for aperiodic CSI-RS transmission. This advantage helps theterminal to use the aperiodic CSI-RS regardless of positions. Inaddition, when the terminal using option 1 for time/frequency resourcedefinition is dynamically allocated an aperiodic CSI-RS in a specificsubframe (full-band), subband or RB, if the corresponding subframetransmits a signal for synchronization (PSS/SSS), transmits SIB1(SystemInformationBlockType1) information containing system information,or is a paging subframe, it can be assumed that all or some of thescheduled information is not transmitted in the region where theaperiodic CSI-RS is allocated.

Second Embodiment

The following options are possible for setting the unit for transmittingaperiodic CSI-RS resources described in the first embodiment.

1. Option 1 for defining the unit for aperiodic CSI-RS resourcetransmission: allocation and transmission based on the full band

2. Option 2 for defining the unit for aperiodic CSI-RS resourcetransmission: allocation and transmission based on specific subband

3. Option 3 for defining the unit for aperiodic CSI-RS resourcetransmission: allocation and transmission based on specific bandwidthpart

4. Option 4 for defining the unit for aperiodic CSI-RS resourcetransmission: allocation and transmission based on specific RGB

5. Option 5 for defining the unit for aperiodic CSI-RS resourcetransmission: allocation and transmission based on specificnon-contiguous RBs

6. Option 6 for defining the unit for aperiodic CSI-RS resourcetransmission: allocation and transmission based on specific contiguousRBs

Option 1 for defining the transmission unit is to allocate and transmitthe aperiodic CSI-RS over the full band. In this option, as the CSI-RSis always transmitted in the full band like the existing periodicCSI-RS, it is not necessary to dynamically transmit additionalinformation except for the indication of aperiodic CSI-RS transmission.Because the CSI-RS is always measured in the full band and the channelstatus information is generated as in the conventional terminaloperation, the operation of the terminal is very similar to theconventional one. However, as the aperiodic CSI-RS must always beallocated and transmitted in the full band, this option isdisadvantageous in terms of efficiency in CSI-RS allocation andtransmission.

Option 2 for defining the transmission unit is to allocate and transmitthe aperiodic CSI-RS in a specific subband. In channel status reporting,the size of the subband depends on the system bandwidth supported by thesystem. Table 5 shows the subband sizes according to the systembandwidth settings.

TABLE 5 System Bandwidth subband Size N_(RB) ^(DL) (k) 6-7 NA  8-10 411-26 4 27-63 6  64-110 8

Subband Size (k) vs. System Bandwidth

The number of subbands varies depending on the system bandwidthsettings. For example, in the case of 50 RBs, according to the abovetable, 6 RBs are set as one subband, so that there are 9 subbands. Forthis setting, a 9-bit field can be used as a bitmap. In this option, asthe estimation range of the terminal is smaller than that of the fullband, it is possible to reduce the channel estimation complexity of theterminal. The estimation range is the same as the existing unit forsubband channel estimation, so that the terminal can use the existinghardware as it is. In addition, CSI-RS resources can be flexibly usedfor each subband. However, RRC or L1 signaling may be required.

Option 3 for defining the transmission unit is to allocate the aperiodicCSI-RS in a specific bandwidth part. Table 6 shows the bandwidth partsused in existing periodic channel status reporting.

TABLE 6 System Bandwidth subband Size k Bandwidth Parts N_(RB) ^(DL)(RBs) (J) 6-7 NA NA  8-10 4 1 11-26 4 2 27-63 6 3  64-110 8 4

Subband Size (k) and Bandwidth Parts (J) vs. System Bandwidth

FIG. 5 depicts operations of the terminal to periodically report thechannel state using a bandwidth part.

In FIG. 5, the terminal divides the entire subbands into J bandwidthparts according to the system bandwidth as shown in the above table,reports the preferred subband position for each bandwidth part, andreports the PMI and the CQI corresponding to the preferred subband tothe base station. Allocating the aperiodic CSI-RS based on the bandwidthpart requires a smaller degree of freedom than the increased degree offreedom due to subband support. Hence, aperiodic CSI-RS transmission canbe performed in a partial band other than the full band with a smallamount of configuration information. When option 2 for defining thetransmission unit is utilized, the terminal can select a specificsubband within a bandwidth part and report the channel state only in theselected subband in the same manner as existing periodic channel statusreporting. This can reduce the amount of uplink data transmissionrequired by the terminal for aperiodic channel status reporting.

Option 4 for defining the transmission unit is to allocate and transmitthe aperiodic CSI-RS in a specific RBG. In channel status reporting, theRGB size depends on the system bandwidth supported by the system. Table7 shows the subband sizes according to the system bandwidth settings.

TABLE 7 Bandwidth (#RBs) RBG size (P) ≤10 1 11-26 2 27-63 3  64-110 4

RBG Size (P) vs. System Bandwidth

The size of the RBG varies depending on the system bandwidth settings.For example, in the case of 50 RBs, according to the above table, 3 RBsare set as one RBG, so that 18 subbands exist. For this setting, an 18bit field can be used as a bitmap. In this case, as the estimation rangeof the terminal is smaller than the full band, the channel estimationcomplexity of the terminal can be reduced. In addition, the CSI-RSresources can be flexibly used in units of RBGs smaller than subbands,and existing downlink resource allocation type 0 can be reused.

FIG. 6 depicts downlink resource allocation type 0.

As shown in FIG. 6, in resource allocation type 0, resources areallocated in units of RBGs determined according to the system bandwidth.For resource allocation based on type 0, the base station uses bits tonotify the resource allocation type. For actual resource allocation, theRBG size corresponding to the system bandwidth size in Table 6 is used.The terminal can be allocated an RBG of a corresponding size using abitmap of size |N_(RB) ^(DL)IP| and can receive the downlink data viathe corresponding resource. Likewise, to notify the terminal of whetherthe aperiodic CSI-RS is to be transmitted in a specific RBG, the basestation can allocate the aperiodic CSI-RS for each RBG according to thecorresponding option. However, RRC or L1 signaling may also be required.

Option 5 for defining the transmission unit is to allocate and transmitthe aperiodic CSI-RS via specific non-contiguous RBs. This optionsupports aperiodic CSI-RS transmission for each non-contiguous RB,thereby increasing the flexibility of resource usage. However, thisoption may increase the signaling overhead for delivery. Here, downlinkresource allocation type 1 may be reused for option 5 for defining thetransmission unit.

FIG. 7 depicts downlink resource allocation type 1.

As shown in FIG. 7, for resource allocation based on type 1, the basestation uses bits to notify the resource allocation type. As thesignaling overhead excessively increases when resources are allocatedfor each RB at one time for the full band, the resources can be dividedinto two parts by the offset for transmission. Type 1 uses the sameamount of signaling as type 0. To this end, the terminal may beallocated corresponding RBs using a bitmap of size (|N_(RB)^(DL)IP|-[log₂(P)]-1), which is a value obtained by subtracting[log₂(P)] bits for selecting the subset and 1 bit for selecting theoffset from the bitmap size |N_(RB) ^(DL)IP| for type 1, and may receivethe downlink data via the corresponding resource. By reusing the methodof downlink resource allocation type 1, the base station can transmitthe aperiodic CSI-RS to the terminal. Here, the method may be RRC or L1signaling. In addition, unlike downlink data allocation, aperiodicCSI-RS transmission through non-contiguous RB allocation has nounnecessary overhead for CSI-RS transmission such as MCS for eachcodeword, more DCI bits can be configured compared with downlink dataresource allocation. In this case, it is also possible to use afull-size bitmap except for the offset.

Option 6 for defining the transmission unit is to allocate and transmitthe aperiodic CSI-RS via specific contiguous RBs. In this option, unliketransmitting the aperiodic CSI-RS via non-contiguous RBs, signalingoverhead is reduced compared to other allocation methods because onlythe start RB position and its length or the end RB position arenotified. However, the aperiodic CSI-RS is always transmitted viacontiguous RBs only. Hence, when it is determined that the efficiency ofthe terminal is high in a noncontiguous RB or subband, only a specificlocation is selected or the aperiodic CSI-RS is transmitted via anunnecessarily large number of bands. In this case, downlink resourceallocation type 2 may be reused for option 6 for defining thetransmission unit.

FIG. 8 depicts downlink resource allocation type 2.

As shown in FIG. 8, to allocate resources based on type 2, the basestation uses 1 bit to indicate whether resources are allocated in theform of a localized virtual resource block (LVRB) or a distributedvirtual resource block (DVRB). Based on this, the start RB position andthe length are notified through the resource indication value (RIV).Here, the start position and the length can be obtained according to theDCI format as shown in Equation 1.

For DCI format 1A, 1B and 1D,

${RIV} = \left\{ \begin{matrix}{{N_{RB}^{DL}\left( {L_{CRBs} - 1} \right)} + {RB}_{start}} & {\left( {L_{{CRB}_{s}} - 1} \right) \leq \left\lfloor {N_{RB}^{DL}/2} \right\rfloor} \\{{N_{RB}^{DL}\left( {N_{RB}^{DL} - L_{CRBs} + 1} \right)} + \left( {N_{RB}^{DL} - 1 - {RB}_{start}} \right)} & {otherwise}\end{matrix} \right.$

For DCI format 1C,

                                      Equation  1${RIV} = \left\{ {{\begin{matrix}{{N_{VRB}^{\prime\;{DL}}\left( {L_{CRBs}^{\prime} - 1} \right)} + {RB}_{start}} & {\left( {L_{CRBs} - 1} \right) \leq \left\lfloor {N_{RB}^{DL}/2} \right\rfloor} \\{{N_{VRB}^{\prime\;{DL}}\left( {N_{VRB}^{\prime\;{DL}} - L_{CRBs}^{\prime} + 1} \right)} + \left( {N_{YRB}^{\prime\;{DL}} - 1 - {RB}_{start}^{\prime}} \right)} & {otherwise}\end{matrix}{where}\mspace{14mu} R\text{?}} = {{R{\text{?}/\text{?}}\mspace{25mu}\text{?}} = {{{L_{CRB}/\text{?}}\mspace{25mu}\text{?}} = {\left\lfloor {\text{?}/\text{?}} \right\rfloor\text{?}\text{indicates text missing or illegible when filed}}}}}\mspace{275mu} \right.$

Here, [log₂(N_(RB) ^(DL)(N_(RB) ^(DL)+1)/2)] bits and[log₂([N_(VRB,gap1) ^(DL)/N_(RB) ^(step)]·([N_(VRB,gap) ^(DL)/N_(RB)^(step)]+1)/2] bits are used for resource allocation.

Although only downlink resource allocation is described in theembodiment of the present invention, the above-mentioned signaling canalso be applied to uplink resource allocation based on the sameprinciple. In addition, although the resource allocation information inthe current LTE/LTE-A system is transmitted through the DCI being L1,the above method can be applied to the configuration through RRCsignaling as well.

Third Embodiment

In option 2 for defining time/frequency resources required for aperiodicCSI-RS transmission described in the first embodiment, as describedbefore, the PDSCH is not transmitted to the terminal in a subframescheduled for aperiodic CSI-RS transmission. Hence, the resourcesrequired for PDSCH transmission and the resources required for DMRStransmission for PDSCH decoding can be used for the CSI-RS. Here, thebase station notifies the OFDM symbols needed for PDCCH transmission viathe PCFICH, and the corresponding resource cannot be used in thesubframe or RB necessary for aperiodic CSI-RS transmission because thePDCCH is to be transmitted. In addition, the CRS cannot be used foraperiodic CSI-RS transmission because it is commonly used by allterminals of the base station for PDSCH decoding, synchronization withthe base station, and RRM. However, in LTE Release 12, subframes exceptfor FDD subframe 0, 4, 5 or 9 and TDD subframe 0, 1, 5 or 6 may beconfigured as a multicast-broadcast single-frequency network (MBSFN)subframe by using the RRC configuration. In the corresponding subframe,the CRS is not transmitted in the PDSCH region except for the PDCCHregion, and thus the CSI-RS region can be increased.

As described above, the CSI-RS resources available in one RB or subframeproposed in the present invention may be changed according to PCFICHtransmission, MBSFN configuration, and the subframe index. In existingperiodic CSI-RS transmission using 1, 2, 4 or 8 ports, as resourcesusable for CSI-RS transmission are always fixed, the transmission ispossible by defining one port index for each antenna. As periodic CSI-RStransmission using 12 or 16 ports is also based on existing resources,the transmission is possible by combining existing 4-port or 8-portCSI-RSs. However, in the case of the method proposed in the presentinvention, as the resources that can be transmitted are changed, itcannot be supported by the existing fixed port definition. Hence, a newrule is required for mapping between resources and ports.

FIG. 9 depicts a situation where the aperiodic CSI-RS RB or subframeproposed in the present invention is transmitted.

In FIG. 9, the base station configures terminals with the periodicCSI-RS. As the existing LTE terminal does not support the aperiodicCSI-RS, a periodic CSI-RS should be transmitted to the LTE terminal forreporting channel state information. Even a terminal supporting newaperiodic CSI-RS transmission can report coarse channel stateinformation by allocating a small number of CSI-RS ports usingvirtualization or beamforming. The base station can determine whether aterminal requires aperiodic CSI-RS transmission, and allocate anaperiodic CSI-RS to the terminal requiring aperiodic CSI-RStransmission. Hence, as shown in FIG. 9, the periodic CSI-RS and theaperiodic CSI-RS may be transmitted in different subframes, but may betransmitted in the same subframe according to the channel state of theterminal.

In this embodiment, the base station and the terminal identify the REsavailable for the aperiodic CSI-RS in the corresponding RB. Here, CSI-RSREs can be secured by excluding all or some REs for the PDCCH, CRS,PCFICH, PHICH, PSS, SSS and paging. As the PDSCH is not transmitted inthe corresponding RB, the DMRS need not be transmitted. Therefore, inoption 1 for defining port indexes proposed in the present invention,the ports are indexed after securing the available REs. The base stationshould transmit the terminal the k-th frequency RE and the position ofthe 1-th time symbol from which the CSI-RS port starts. The startingfrequency and the time symbol position can be indicated by a pair (k,l)with respect to the whole RB. For example, in one RB, the 0-thsubcarrier and the 4-th time symbol may be represented by (0,4), and the6-th subcarrier and 7-th symbol may be represented by (6,7). Here, insetting the time and frequency position, it is equally effective tonotify the time symbol first and notify the frequency position later.Also, it is possible to indicate (k, l) pairs with respect to the slotother than one RB. For example, (0,4) may be represented by (0,4) ns=0,and (6, 7) may be represented by (6,0) ns=1. In addition, the above twomethods may be represented by using one parameter. For example, index 0can represent (0,0), and index 1 can represent (1,0). This can also berepresented by an equation indicating the relationship between theparameter and (k,l). Equation 2 represents such a relationship.

With respect to the RB, k=mod(I,12),l=[I/14]

With respect to the slot, n _(s) =[I/64],k=mod(I,12),l=[mod(I,64)/7]  Equation 2

The CSI-RS port index start resource proposed in the present inventioncan be specified as follows.

1. Option 1 for specifying the start CSI-RS resource: use the DCI

2. Option 2 for specifying the start CSI-RS resource: specify theavailable resource via RRC

3. Option 3 for specifying the start CSI-RS resource: specify theavailable resource separately for normal and MBSFN subframes via RRC

Option 1 for specifying the start resource is a scheme using the DCI.The base station notifies the terminal of the index of the correspondingresource position, and the terminal receives the index and identifiesthe resource based on the number of antenna ports. However, as there aremany possible positions that can be set as the start position, theoverhead can be large (168 bits are required when all REs areavailable). If the CSI-RS allocation unit is a slot or a smaller unitother than the RB, as the number of bits can be reduced, the use of thisoption can be considered. In this case, the aperiodic start resourceconfiguration is delivered via the DCI, but the configuration about thenumber of CSI-RS antenna ports required for the terminal, subsampling,the number of antenna ports after subsampling, P_(C) value, codebooksubset restriction, and the like can be set through RRC.

Option 2 for specifying the start resource is a scheme using RRC. Thebase station notifies the corresponding resource position in advance viaRRC, and the terminal can identify the resource together with the numberof antenna ports. These fields may be named as ResourceConfig-r14 usingfields similar to existing periodic CSI-RS resources. However, as theterminal can receive the aperiodic CSI-RS only at a preset position, theCSI-RS resource efficiency can be relatively lowered. In this case, itis also possible to increase the degree of freedom of aperiodic CSI-RStransmission by providing multiple candidates for aperiodic CSI-RStransmission. To this end, the base station may notify the terminal ofthe candidates being transmitted via the DCI, and the terminal canrecognize that the aperiodic CSI-RS is transmitted according to theindicated setting among multiple settings. Tables 8 and 9 illustrate themapping between the DCI fields and aperiodic CSI-RS configuration.

TABLE 8 AP-CSI-RS indicator Notification 00 First aperiodic CSI-RSconfiguration set by RRC information 01 Second aperiodic CSI-RSconfiguration set by RRC information 10 Third aperiodic CSI-RSconfiguration set by RRC information 11 Fourth aperiodic CSI-RSconfiguration set by RRC information

Allocation DCI signaling with separate bit for aperiodic CSI-RStransmission

TABLE 9 AP-CSI-RS indicator Notification 00 No aperiodic CSI-RStransmission 01 First aperiodic CSI-RS configuration set by RRCinformation 10 Second aperiodic CSI-RS configuration set by RRCinformation 11 Third aperiodic CSI-RS configuration set by RRCinformation

Allocation DCI signaling without separate bit for aperiodic CSI-RStransmission

Table 8 illustrates allocation DCI signaling when there is a separatebit for aperiodic CSI-RS transmission. The base station uses anadditional 1 bit to indicate whether the aperiodic CSI-RS istransmitted. With an additional bit, there is no need to indicate theabsence of aperiodic CSI-RS transmission in this signaling, and two bitscan be used to indicate one of four aperiodic CSI-RS configurations.

Table 9 illustrates allocation DCI signaling when there is no separatebit for aperiodic CSI-RS transmission. As the base station does not usean additional 1 bit indicating whether the aperiodic CSI-RS istransmitted, the corresponding field must also be included in theindication, and two bits can be used to indicate up to three aperiodicCSI-RS configurations.

Although the above example is using two bits, the number of indicationscan be increased by using 3 bits, 4 bits, and so on. In addition to theaperiodic start resource configuration, the number of CSI-RS antennaports required for the terminal, application of subsampling, the numberof antenna ports after subsampling, P_(C) value, codebook subsetrestriction, and the like can be set as separate fields through RRC.

However, when an MBSFN subframe is configured, the port mapping and theresource position in the corresponding RB may vary depending on thesubframe location, and all possible settings must be provided for eachcase. Here, if the number of possible settings is small, the degree offreedom decreases; and if there is a large number of possible settings,the DCI overhead for selection increases, which may reduce theefficiency of the aperiodic CSI-RS resource transmission.

Option 3 for specifying the start CSI-RS resource is a method specifyingthe available resource separately for normal and MBSFN subframes viaRRC. This option is basically similar to option 2 for specifying thestart resource, but the DCI overhead can be reduced by separatelyhandling the normal subframe and the MBSFN sub-frame. The terminal maycheck whether the subframe in which the aperiodic CSI-RS is configuredis a normal subframe or an MBSFN subframe, and identify the aperiodicCSI-RS configuration among the settings corresponding to the indicatedsubframe. For example, if four of the eight advance settings are to beused for the MBSFN subframe and four for the normal subframe, 3 DCI bitsmust always be transmitted in option 2 while 2 DCI bits can betransmitted in option 3. However, option 2 can be freely adjustedregardless of which subframe the 8 settings are used for while option 3should always divide the settings by four, which may result inrestrictions on aperiodic CSI-RS transmission.

The method of defining the port index based on the start resourceconfiguration in the CSI-RS RB or subframe proposed in the presentinvention can be divided into the following two cases according to thepossibility of simultaneous transmission to the legacy terminal.

1. Option 1 for CSI-RS RB or port index definition: the port index isassigned to the corresponding transmittable resource according tofrequency and time resources

2. Option 2 for CSI-RS RB or port index definition: the correspondingtransmittable resources are divided into legacy CSI-RS resources and newCSI-RS resources and the port index is separately assigned for eachresource type according to frequency and time resources

FIG. 10 illustrates an example of defining port indexes based on option1 for port index definition and assigning the port index to theterminal.

With reference to FIG. 10, for the frequency, the frequency resources ofthe RBs can be divided in half and the ports can be alternately assignedbased on the position of the frequency RE and the symbol indicated bythe start resource setting method described before. In the case of timesymbol, port assignment is performed using two time symbols from thecorresponding time symbol for CDM2, and using four time symbols forCDM4. For example, in FIG. 10, the base station configures terminal 0with 32 antenna ports based on CDM2 for (k,l)=(0,2). Based on thisinformation, the terminal may divide one RB in half by using two timesymbols, and may map ports 0 and 1 to k=0, ports 2 and 3 to k=6, ports 4and 5 to k=1, ports 6 and 7 to k=7, and so on. Here, as there are only12 frequency resources in one RB, it is not possible to map all the 32antenna ports to two time symbols. Hence, up to ports 22 and 23 aremapped to the corresponding time symbol, and ports 24 and later aremapped to the next time symbol. Note that the time symbol via which theCRS is transmitted is not used together with the time symbol via whichthe CRS is not transmitted and only the CRS transmitting symbols areused together. This means that the REs carrying the CRS must consume alot of power for the CRS, so that the available transmission power canbe relatively small compared to the normal REs. The REs carrying the CRSmay be different from the normal REs in terms of the power ratio betweenthe CSI-RS and the PDSCH (P_(C)value). Therefore, it is desirable tocollect the REs carrying the CRS and map the port index thereto. Theconfiguration and use of time and frequency resources for the CRS can bedescribed based on terminal 3 in FIG. 10. Terminal 3 is configured withthe start position indicated by (k,l)=(1,4) based on CDM2. As thecorresponding position is a position where the CRS is transmitted, theterminal groups other CRS symbols and maps the CSI-RS port thereto basedon CDM2.

In FIG. 10, terminal 3 uses symbol 4 and symbol 11 via which the CRS istransmitted as a bundle. However, it is also possible to combine nearbyCRS symbols. When using nearby symbols as a bundle, the performance canbe equalized because the time symbol distance between the two resourcesis the same within the CSI-RS resources in which the CRS symbol istransmitted. However, as shown in FIG. 10, using the resources that are7 symbols away may degrade performance compared to using nearby symbols7 and 8 together. Additionally, in the case of CDM4, all four timesymbols carrying the CRS are used as a bundle. This method can beefficiently used when only the aperiodic CSI-RS is allocated to one RBfor transmission. However, as shown in FIG. 9, when the existingperiodic CSI-RS and the aperiodic CSI-RS need to be allocated andtransmitted in an overlapping manner, resource utilization may becomeinefficient. As described above, CRS symbols and normal symbols maydiffer in terms of power usage. A plurality of P_(C) values may be setfor the CSI-RS configuration so that different P_(C) values can beapplied depending on the symbol corresponding to the resource. Forexample, it is possible to use a P_(C) value corresponding to the CRSsymbol when the base station indicates the symbol in which the CRS istransmitted, and use a P_(C) value corresponding to the normal symbolwhen the CSI-RS is transmitted via a normal symbol.

FIG. 11 illustrates an example of defining port indexes based on option2 for port index definition.

The method of FIG. 11 is basically the same as the method of FIG. 10described above except that the same approach as before is applied tothe REs used for the legacy CSI-RS. When the terminal is allocated alegacy CSI-RS RE as the start resource, the port is mapped only to thelegacy CSI-RS REs in the same manner as before. For example, in FIG. 11,when terminal 0 is allocated 16 ports, existing CSI-RS RE resourcesother than the above frequency resources are used after port 4/5 andport 6/7 are allocated. Although this method is somewhat complicated inport indexing, it can also be used for transmission to the legacyterminal.

In the above embodiments, the port mapping method is assumed to set onetransmission position for transmission. However, like 12 and 16 CSI-RSport configurations in Release 13, it is possible to generate 12, 16 ormore CSI-RS ports such as 22, 24, 26, 28, 30, and 32 CSI-RS ports bysetting a plurality of start positions and a number of antenna ports foreach start position and combining the corresponding positions. In theabove description, ports 0, 1, . . . , 15 are used, but they can be usedas CSI-RS ports 15, 16, . . . , 30 as in LTE. It is also possible togenerate 16 or more CSI-RS ports such as 22, 24, 26, 28, 30, and 32CSI-RS ports.

In addition, the above configuration method can be used for configuringnot only the non-zero power (NZP) CSI-RS but also the zero power (ZP)CSI-RS and the CSI-IM. Here, in the case of the ZP CSI-RS or the CSI-IM,the number of antenna ports is fixed to 4 and thus no antennaconfiguration is needed, and subsampling may be not applied. Inaddition, when the aperiodic CSI-IM includes both a CSI-RS relatedresource and a CSI-IM related resource in one field for each aperiodicCSI-RS, it is also possible to measure the channel at the CSI-RSposition and measure the interference at the CSI-IM position when thecorresponding field is indicated.

In addition, when the corresponding resource is transmitted in a partialband (RB, RBG, subband, and bandwidth part) other than the full band, anew DCI format may be defined to allocate it. The corresponding formatcan be defined using existing resource allocation types 0, 1 and 2 asproposed in the present invention. The aperiodic CSI-RS configurationmay be based on the UL DCI format because it requires aperiodic channelstatus reporting. Here, to indicate uplink data transmission allocationand aperiodic CSI-RS transmission, one DCI format may be transmitted tothe terminal or two DCI formats may be simultaneously transmitted to theterminal. In this case, an additional ID or RNTI may be required foraperiodic CSI-RS transmission. Thereby, the terminal may be allocatedCSI-RS resources and may report the channel state by applying theindicated number of antenna ports, subsampling, the number of antennaports after subsampling, P_(C) value, codebook subset restriction, andthe like. Here, under an agreement that the aperiodic CSI-RS istransmitted in the subframe where the DCI is transmitted, the subframeconfiguration may be not included in the aperiodic CSI-RS configuration.

Fourth Embodiment

To perform aperiodic CSI-RS transmission using existing CSI-RS REsaccording to option 1 for time and frequency resource definitiondescribed in the first embodiment, zero power (ZP) CSI-RS informationshould be configured to transmit correct rate matching information tothe terminal receiving both the CSI-RS and the PDSCH. The ZP CSI-RSresource can be configured according to the following two schemes.

1. Option 1 for ZP CSI-RS resource definition: configure the ZP CSI-RSin advance via RRC and use it as a pool for aperiodic CSI-RStransmission

2. Option 2 for ZP CSI-RS resource definition: dynamically configure theZP CSI-RS via the DCI according to the situation and use it as a poolfor aperiodic CSI-RS transmission

Option 1 for ZP CSI-RS resource definition is a method that creates apool for aperiodic CSI-RS transmission and allocates the aperiodicCSI-RS only in the pool.

FIG. 12 shows an example where the base station creates a pool for theaperiodic CSI-RS and assigns the pool to each terminal.

With reference to FIG. 12, the base station can configure in advance aCSI-RS pool as shown in the form of a rectangle through the RRC setting.As there is no limit to the number of ZP CSI-RSs that can be configuredin the current LTE system, the base station can allocate a large numberof ZP CSI-RSs to the legacy terminal. Hence, a CSI-RS pool for aperiodicCSI-RS transmission can be set for the legacy terminal that does notsupport the aperiodic CSI-RS.

As the terminal knows in advance that the ZP CSI-RS is applied to aspecific position, when the PDSCH is transmitted, it may determine thatthe PDSCH is not transmitted via the corresponding resource and performrate matching accordingly. In the corresponding ZP CSI-RS, the basestation can non-periodically allocate only a CSI-RS resource to theterminal. In this case, to non-periodically allocate the NZP CSI-RS, thebase station must dynamically transmit the corresponding configurationto the terminal. In LTE, if the resource positions indicated by the ZPCSI-RS configuration and the NZP CSI-RS configuration are the same, theNZP CSI-RS configuration takes precedence. When the aperiodic CSI-RS isallocated, the corresponding resource is regarded by the terminal as theNZP CSI-RS, and thus it is possible to measure the channel in thecorresponding resource. Although FIG. 12 shows an aperiodic CSI-RStransmission to only one terminal with a CSI-RS pool occupying onesubframe, the aperiodic CSI-RS may be transmitted to multiple terminals.Also, as described above, the transmission unit may be a full subband ora partial subband. If the terminal supports aperiodic CSI-RStransmission using the appropriate method, for simultaneous support ofthe legacy terminal, the terminal may not expect transmission of anaperiodic CSI-RS resource that does not overlap with the ZP CSI-RS.Configuring the CSI-RS pool based on the semi-static ZP CSI-RSconfiguration has an advantage that it can operate smoothly with thelegacy terminal. However, as the semi-static ZP CSI-RS must be allocatedin advance for this purpose, the number of REs for PDSCH transmissioncan be reduced. This may cause a failure in achieving the effect of theaperiodic CSI-RS (i.e., increasing the system performance throughefficient resource utilization).

Option 2 for ZP CSI-RS resource definition is a method that dynamicallyconfigures the ZP CSI-RS according to the situation through the DCI.Table 10 shows a resource configuration example for the ZP CSI-RSconfiguration.

TABLE 10 A-CSI-RS-ConfigZP-r14 ::= SEQUENCE {  a-csi-RS-ConfigZPId-r14 A-CSI-RS-ConfigZPId-r14,  resourceConfigList-r11 BIT STRING (SIZE(16)),  subframeConfig-r11  INTEGER (0..154),  ... }

Example of RRC settings for aperiodic ZP CSI-RS configuration

Here, the base station can deliver the corresponding configuration inthe following manner.

1. Option 1 for dynamic ZP CSI-RS resource transmission: configure theresource via a signal of 1 bit

2. Option 2 for dynamic ZP CSI-RS resource transmission: configure theresource via a signal of 2 or more bits

When the ZP CSI-RS resource is configured through a 1-bit signal usingoption 1 for dynamic ZP CSI-RS resource transmission, the terminal cancheck only the presence or absence of a ZP CSI-RS in the correspondingresource. In this method, when there is an aperiodic ZP CSI-RS, theterminal must assume that the ZP CSI-RS is always present in allsubframes for all downlink resources allocated to the terminal for PDSCHtransmission. In this case, even if the base station does not need totransmit the aperiodic NZP CSI-RS in all the bands allocated to theterminal, the terminal cannot assume that the PDSCH is transmitted viathe corresponding resources, so that resources may be unnecessarilyconsumed. However, the signaling overhead for dynamic configuration canbe minimized.

When the ZP CSI-RS resource is configured through a signal of 2 or morebits using option 2 for dynamic ZP CSI-RS resource transmission, thenumber of antenna ports and the start resource can be set in advance byRRC as in the third embodiment of the present invention. In this case,the terminal can identify not only the presence or absence of the ZPCSI-RS in the corresponding resource but also the position of theconfigured ZP CSI-RS. In this method, when the aperiodic ZP CSI-RS ispresent, the terminal may check whether there is a ZP CSI-RS in somedownlink resources for PDSCH transmission. This setting is possibleusing an RRC field, and can be considered for all transmission unitsincluding the proposed CSI-RS transmission unit. Thus, the PDSCH can bedecoded by assuming that the ZP CSI-RS is present in the correspondingresource overlapping the PDSCH transmission. This method allows moreflexible and diverse aperiodic ZP CSI-RS transmissions, but it requiresDCI overhead. Here, the transmitted DCI may be a common DCI applied toall the terminals to transmit ZP CSI-RS configuration information to theterminals in common. When using the common DCI, the DCI overhead can bereduced by multicasting the DCI to the terminals receiving the PDSCHrather than separately transmitting the DCI to the individual terminals.As the common DCI is commonly transmitted information, it can betransmitted in the common search space. To maintain the same number ofPDCCH blind decodings as in the existing scheme, the common DCI cancarry the same number of payload bits as the legacy PDCCH. Here, the bitnot carrying information can be fixed to a specific value such as 0or 1. Such multibit aperiodic ZP CSI-RS transmission may be performedbased on Tables 7 and 8 described above. For this common DCItransmission, a ZP CSI-RS RNTI can be introduced. Since the common DCIis no longer UE-specific, it cannot be transmitted based on the RNTI setfor each terminal and may require the corresponding RNTI information.Table 11 below illustrates the common RNTI configuration for ZP CSI-RStransmission.

TABLE 11 ZP-DCI-Config-r14 ::= SEQUENCE {  ...  zp-csi-RS-RNTI  BITSTRING (SIZE (16)),  ... }

ZP CSI-RS RNTI Configuration

The RNTI in the above example is referred to as a ZP CSI-RS RNTI, but itmay also be referred to as a common DCI RNTI or a CSI-RS RNTI. Inaddition to ZP CSI-RS information, the common DCI may include activationinformation of the aperiodic NZP CSI-RS transmission resource andtrigger information of the RS transmission. Aperiodic CSI-RS resourceconfiguration and triggering can be performed in the following threeways.

1. Option 1 for aperiodic CSI-RS resource configuration and triggering:configure a number of aperiodic CSI-RS resources in advance and triggersome of the configured resources

2. Option 2 for aperiodic CSI-RS resource configuration and triggering:configure a number of aperiodic CSI-RS resources in advance, activatesome of the configured resources, and trigger some of the activatedresources

3. Option 3 for aperiodic CSI-RS resource configuration and triggering:configure a number of aperiodic CSI-RS resources in advance, andperiodically transmit the corresponding CSI-RS resource upon activationuntil it is deactivated

Option 1 for aperiodic CSI-RS resource configuration and triggering is amethod that configures a plurality of aperiodic CSI-RS resources inadvance and triggers some of the configured resources. In this method,as a plurality of resources should always be configured dynamically andall the configured resources should be supported, the complexity of theterminal may be relatively large. Option 2 for aperiodic CSI-RS resourceconfiguration and triggering is a method that dynamically transmits onlysome of the configured resources. In this method, as the number oftransmittable CSI-RS resources is relatively small, the terminalcomplexity is reduced compared with option 1, and dynamic CSI-RStransmission is also possible. In option 3 for aperiodic CSI-RS resourceconfiguration and triggering, a plurality of resources are configuredand all or some of them are periodically transmitted based on theconcept of semi-persistent scheduling (SPS). In this method, thehardware change and complexity increase of the terminal are relativelysmall compared with options 1 and 2.

Option 2 and option 3 for aperiodic CSI-RS resource configuration andtriggering can coexist in one system. In this case, the following waysmay be considered to distinguish the settings of trigger options 2 and3.

1. Scheme 1 for setting the CSI-RS type: introduce an RRC fieldindicating whether trigger option 2 or 3 is set

2. Scheme 2 for setting the CSI-RS type: determine according to thepresence or absence of subframe config

Scheme 1 for setting the CSI-RS type is to introduce an RRC fieldindicating whether trigger option 2 or 3 is set. Table 12 belowillustrates an RRC configuration in CSI-RS type setting scheme 1.

TABLE 12 CSI-RS-ConfigNZP-r11 : := SEQUENCE {  csi-RS-ConfigNZPId-r11 CSI-RS-ConfigNZPId-r11,  antennaPortsCount-r11  ENUMERATED {an1, an2,an4, an8},  resourceConfig-r11  INTEGER (0. .31) ,  subframeConfig-r11 INTEGER (0. .154) ,  scramblingIdentity-r11  INTEGER (0. .503) , qcl-CRS-Info-r11  SEQUENCE {   qcl-ScramblingIdentity-r11   INTEGER (0..503) ,   crs-PortsCount-r11 ENUMERATED {n1, n2, n4, spare1},  mbsfn-SubframeConfigList-r11 CHOICE {    release   NULL,    setupSEQUENCE {     subframeConfigList    MBSFN-SubframeConfigList    }   }OPTIONAL -- Need ON  } OPTIONAL,  - - Need OR  . . . ,  [ [csi-RS-ConfigNZPId-v1310 CSI-RS-ConfigNZPId-v1310  OPTIONAL,  -- Need ON ] ]  [ [ aperiodic-RS-Type-r14 ENUMERATED {one-shot, multi-shot } OPTIONAL -- Need ON  ] ] }

Illustration of CSI-RS Type Setting Scheme 1

In addition to the existing Release 13 LTE CSI-RS configuration field,the terminal may be configured with the aperiodic-RS-Type-r14 field. Ifthe aperiodic-RS-Type-r14 field is not configured, the terminal maydetermine that this CSI-RS configuration is for the existing periodicCSI-RS other than the aperiodic CSI-RS. If the aperiodic-RS-Type-r14field is configured, the terminal can determine the correspondingresource as a resource that can be activated and deactivated for theaperiodic CSI-RS transmission operation described above. Here, if theaperiodic-RS-Type-r14 field is set as one-shot, the terminal maydetermine that the corresponding CSI-RS resource is in the form of theCSI-RS transmitted in one subframe according to trigger option 2described above. In this case, existing subframeconfig-r11 is notrequired and should be ignored. If the aperiodic-RS-Type-r14 field isset as multi-shot, the terminal may determine the corresponding CSI-RSresource as a resource that can be activated or deactivated andtransmitted in multiple subframes according to trigger option 3described above. In this case, when the CSI-RS resource is activated bysubframe config, the CSI-RS is transmitted according to subframe config.

Scheme 2 for setting the CSI-RS type is a method of distinguishingbetween trigger option 2 and trigger option 3 depending on the presenceof subframe config. As described above, trigger options 2 and 3 may notrequire other settings other than subframe config. Hence, if there is nosubframe config in the configuration of Table 9, the terminal maydetermine that the CSI-RS is transmitted in one subframe according totrigger option 2; and if there is subframe config, the terminal maydetermine the corresponding CSI-RS resource as a resource that can beactivated or deactivated and transmitted in multiple subframes accordingto trigger option 3.

To support the aperiodic CSI-RS transmission, theactivation/deactivation operation and the triggering operation may beindicated via DCI or MAC CE signaling. Additionally, in association withthe above-described triggering method, it is possible to supportmultiple CSI-RS transmission methods. One possible way is to allowtrigger option 2 and trigger option 3 to be configured together, andnotify their supportability via the UE capability. Hence, if theterminal supports both trigger option 2 and trigger option 3, the basestation can freely select one of them and configure it; and if the UEcapability of the terminal supports only one option, the base stationmay allow the option to be used. For the above selective support, the UEcapability signal may be supported in the following manner.

In the first UE capability support method, multiple capabilities areindependently set for aperiodic CSI-RS transmission, and when aparticular capability supports aperiodic CSI-RS transmission, one of thetrigger options (e.g., trigger options 2 and 3) is selected according tothe capability. This method can reduce the terminal complexity byallowing the terminal to support one of the two aperiodic CSI-RS schemesrather than supporting both.

In the second UE capability support method, multiple capabilities areindependently set for aperiodic CSI-RS transmission, and when aparticular capability supports aperiodic CSI-RS transmission, a UEcapability signaling field for the option requiring higher complexity isadditionally secured to reduce signaling overhead. For example, triggeroption 2 requires a higher complexity than trigger option 3, and thus itmay be natural for the terminal supporting trigger option 2 to supporttrigger option 3. Hence, if the terminal supports aperiodic CSI-RStransmission and the capability supporting trigger option 2 indicatessupport of trigger option 2, the terminal may support both triggeroption 2 and trigger option 3; and if trigger option 2 is not supported,the terminal may naturally support trigger option 3 only.

In supporting the UE capability, if the terminal does not supportaperiodic CSI-RS transmission, the field for supporting an additionalaperiodic CSI-RS transmission type may be not set or may be ignored evenif it is set.

The UE capability may provide the terminal with only one configurationfield and may be used for all bands or band combinations. It is alsopossible to reduce the hardware complexity of the terminal by providinga separate field for each band or band combination to optimize thehardware for each band or band combination.

In supporting the aperiodic CSI-RS transmission, PQI (PDSCH-RE-mappingquasi co-location information) supported by TM10 may be considered.Table 13 below shows a PQI information setting field.

TABLE 13 PDSCH-RE-MappingQCL-Config-r11 ::=  SEQUENCE { pdsch-RE-MappingQCL-ConfigId-r11  PDSCH-RE-MappingQCL-ConfigId-r11, optionalSetOfFields-r11  SEQUENCE {   crs-PortsCount-r11  ENUMERATED{n1 , n2, n4, spare1},   crs-FreqShift-r11  INTEGER (0..5),  mbsfn-SubframeConfigList-r11  CHOICE {    release   NULL,    setup  SEQUENCE {     subframeConfigList    MBSFN-SubframeConfigList    }   }     OPTIONAL, -- Need ON   pdsch-Start-r11   ENUMERATED {reserved, n1,n2, n3, n4, assigned}  } OPTIONAL, -- Need OP  csi-RS-ConfigZPId-r11CSI-RS-ConfigZPId-r11,  qcl-CSI-RS-ConfigNZPId-r11 CSI-RS-ConfigNZPId-r11 OPTIONAL,-- Need OR  ... }

PQI Information Setting Field

Via the PQI field, the base station transmits the terminal the PDSCHtransmission start time, the ZP CSI-RS information, and the quasico-located NZP CSI-RS information together at the time of thecorresponding transmission. QCL (quasi co-location) is of type A or typeB. For QCL type A, it is assumed that the CRS, CSI-RS and DMRS are QCLedin terms of delay spread, Doppler spread, Doppler shift, and averagedelay. For QCL type B, the CRS can support information about Dopplerspread and Doppler shift only, and other information should be obtainedthrough the CSI-RS. The QCL support for aperiodic CSI-RS transmissionmay be different from the QCL support for periodic CSI-RS transmission.The QCL support for aperiodic CSI-RS transmission may be performed inthe following way.

In the first QCL support method for aperiodic CSI-RS transmission, theQCL assumption is not supported for the corresponding DMRS transmissionin the case of aperiodic CSI-RS transmission. The aperiodic CSI-RStransmission may be full-band transmission, but if the system bandwidthis narrow, the estimation of the corresponding information may belimited. Hence, the corresponding information can be supported throughthe existing CRS or periodic CSI-RS transmission. In this case, theterminal cannot receive the CSI-RS resource or the CSI-RS ID configuredas the aperiodic CSI-RS through the PQI field, and only the existing CRSand periodic CSI-RS transmission should be indicated by thecorresponding field. Hence, even when the terminal generates and reportschannel state information based on the aperiodic CSI-RS, the terminalestimates the delay spread, Doppler spread, Doppler shift, and averagedelay based on the CRS and periodic CSI-RS transmission and decodes theDMRS on the basis of this estimated information.

In the second QCL support method for aperiodic CSI-RS transmission, theQCL assumption for the corresponding DMRS transmission is supported onlyfrom the CRS associated with the CSI-RS indicated by the PQI field inthe case of aperiodic CSI-RS transmission. In this method, the QCLinformation of the corresponding channel can be obtained through theCRS. In this case, unlike estimating information using both the CSI-RSand the CRS, the delay spread, Doppler spread, Doppler shift, andaverage delay are estimated based on the CRS only, and the DMRS isdecoded on the basis of the estimated information. This method isoperable when the CSI-RS set in the PQI field is an aperiodic CSI-RS ora CSI-RS ID indicating a resource configured as an aperiodic CSI-RS.

In the third QCL support method for aperiodic CSI-RS transmission, theexisting QCL assumption of QCL type A or type B is maintained even inthe case of aperiodic CSI-RS transmission. With this method, theadditional hardware implementation complexity of the terminal can beminimized. In this option, the base station estimates the delay spread,Doppler spread, Doppler shift, and average delay based on the aperiodicCSI-RS different from the existing periodic CSI-RS, and decodes the DMRSbased on this estimated information. Hence, the CSI-RS resourceindicated by the PQI field or indicated by the CSI-RS ID supportsaperiodic CSI-RS transmission, and the terminal may preform estimationand decode the DMRS based on the corresponding aperiodic CSI-RS.

Different QCL support schemes may be considered for the three QCLsupport methods and the three aperiodic CSI-RS trigger options. Forexample, in aperiodic CSI-RS trigger option 1 or 2, as CSI-RStransmission is assumed in one subframe, it may be difficult to obtainQCL information, especially Doppler-related information. Hence, forthese trigger options, the first or second QCL support method can beused. In the case of trigger option 3, as the CSI-RS is periodicallytransmitted in a given interval after activation, relatively sufficientestimation performance can be obtained, and thus QCL may be supported ina conventional manner. In such a case, if the CSI-RS resource or theCSI-RS ID indicated by the base station to the terminal through the PQIis an aperiodic CSI-RS transmitted in one subframe according to triggeroption 2, this setting may be not allowed. If the CSI-RS resource or theCSI-RS ID indicated by the base station to the terminal through the PQIis an aperiodic CSI-RS transmitted in one subframe according to triggeroption 3, this setting may be allowed. Even if the base station isallowed to configure the CSI-RS according to CSI-RS trigger option 1 or2, the terminal may determine the configuration to be wrong and ignoreit. In addition, the combination of these QCL methods or options mayvary depending on the amount of transmission in the aperiodic CSI-RStransmission. For example, when the transmission time is set in advancefor the CSI-RS transmission resource, if the set transmission timeexpires, the legacy QCL setting can be applied. For the PQI indicationand QCL configuration, the corresponding method can be similarly appliedto the ZP CSI-RS configuration. In other words, the ZP CSI-RSconfiguration set by trigger option 3 indicates the ZP CSI-RS using thePQI, and the ZP CSI-RS configuration set by trigger options 1 and 2triggers using a separate DCI field. It may be possible to trigger theZP CSI-RS configuration set by trigger option 3 using at least one of aPQI field or a separate DCI field.

The combination of these QCL methods or options may vary depending onthe RRC setting of the base station. Table 14 below shows the existingQCL configuration field.

TABLE 14 PDSCH-ConfigDedicated-v1130 ::=   SEQUENCE { dmrs-ConfigPDSCH-r11  DMRS-Config-r11  OPTIONAL, --Need ON qcl-Operation ENUMERATED {typeA, typeB} OPTIONAL, -- Need OR re-MappingQCLConfigToReleaseList-r11RE-MappingQCLConfigToReleaseList-r11 OPTIONAL, -- Need ON re-MappingQCLConfigToAddModList-r11  RE-MappingQCLConfigToAddModList-r11OPTIONAL  -- Need ON }

Existing QCL Configuration Field

As described above, the base station notifies the QCL type (i.e., type Aor type B) for the corresponding transmission to the terminal, and theterminal obtains information regarding the delay spread, the Dopplerspread, the Doppler shift, and the average delay accordingly. The QCLconfiguration can be added for aperiodic CSI-RS transmission, and thefirst QCL support method and the second QCL support option, which arenot supported before, can be indicated respectively by QCL type C andtype D. Table 15 below illustrates a QCL configuration field foraperiodic CSI-RS transmission.

TABLE 15 PDSCH-ConfigDedicated-v14 ::= SEQUENCE {  dmrs-ConfigPDSCH-r14DMRS-Config-r11 OPTIONAL, --Need ON  qcl-Operation-r14  ENUMERATED{typeA, typeB, typeC } OPTIONAL, -- Need OR re-MappingQCLConfigToReleaseList-r11RE-MappingQCLConfigToReleaseList-r11  OPTIONAL,  -- Need ON re-MappingQCLConfigToAddModList-r11   RE-MappingQCLConfigToAddModList-r11 OPTIONAL -- Need ON }

QCL configuration field considering aperiodic CSI-RS transmission

In Table 15, one of the first and second methods for QCL support hasbeen added as QCL type C (there are three QCL types), but both methodsmay be considered and QCL type D may also be supported.

In the case of trigger option 1 or 2, as described above, the QCLindication may be not issued through the PQI. This means that thecorresponding CSI-RS cannot be used for CoMP transmission. Hence, whenthe aperiodic ZP CSI-RS described above is configured using one bit ortwo or more bits as illustrated in Table 7 or Table 8, thisconfiguration can be received as follows through the DCI.

1. DCI transmission option 1 for the aperiodic ZP CSI-RS configuration:add an additional bit to the existing DCI field

2. DCI transmission option 2 for the aperiodic ZP CSI-RS configuration:reuse the existing PQI field positions

3. DCI transmission option 3 for the aperiodic ZP CSI-RS configuration:use the existing PQI field or a new DCI indication depending on theconfiguration of the base station

In DCI transmission option 1, an additional bit is added to the existingDCI field for reception. When the base station configures an aperiodicCSI-RS based on trigger option 1 or 2, the terminal cannot support CoMPtransmission based on the aperiodic CSI-RS. Hence, to support CoMPtransmission, the CSI-RS based on the existing periodic CSI-RS ortrigger option 3 is required. In the case of the terminal thatsimultaneously supports plural types of CSI-RSs, a PQI field for CoMPtransmission and a DCI field for ZP CSI-RS configuration can beseparately set, the ZP CSI-RS configuration indicated by the PQI fieldand the aperiodic ZP CSI-RS indicated by the DCI field can be used incombination according to the situation. The aperiodic ZP CSI-RSconfigurations indicated by the PQI field and a separate DCI field maybe combined in the following way.

1. Method 1 for combining aperiodic ZP CSI-RSs indicated by PQI and DCIfields: perform rate matching in consideration of the two ZP CSI-RSconfigurations.

2. Method 2 for combining aperiodic ZP CSI-RSs indicated by PQI and DCIfields: perform rate matching by selecting the PQI field indication.

3. Method 3 for combining aperiodic ZP CSI-RSs indicated by PQI and DCIfields: perform rate matching by selecting the DCI field indication.

In method 1 for combining aperiodic ZP CSI-RSs indicated by PQI and DCIfields, rate matching is performed in consideration of the two ZP CSI-RSconfigurations. If a terminal simultaneously supports a periodic CSI-RSin one TP and an aperiodic CSI-RS in another TP in a CoMP situation, theterminal needs to consider two ZP CSI-RSs simultaneously. In particular,when the dynamic point selection (DPS) is performed on the frequencydomain, the terminal must perform rate matching by considering two ZPCSI-RS settings at the same time, and thus combination method 1 canimprove the performance by supporting this type of transmission.

In method 2 for combining aperiodic ZP CSI-RSs indicated by PQI and DCIfields, rate matching is performed by selecting the PQI fieldindication. When the terminal simultaneously supports a periodic CSI-RSin one TP and an aperiodic CSI-RS in another TP in a CoMP situation,this method supports only one TP in terms of frequency while givingpriority to the CoMP transmission.

In method 3 for combining aperiodic ZP CSI-RSs indicated by PQI and DCIfields, rate matching is performed by selecting the DCI fieldindication. When the terminal simultaneously supports a periodic CSI-RSin one TP and an aperiodic CSI-RS in another TP in a CoMP situation,this method supports only one TP in terms of frequency while givingpriority to the data transmission at the main TP sending the CRS to theterminal.

Here, combination method 2 and combination method 3 can be used togetheraccording to the DCI field indication. For example, when the indicationfield of Table 8 is used for ZP CSI-RS transmission, priority is givento the indication of the PQI field if the DCI field is set to a value of‘00’ indicating no ZP CSI-RS transmission; and priority is given to theindication of the DCI field if the DCI field is set to any other value.In addition, the base station may transmit a 1-bit signal to enable theterminal to determine the field to be used for ZP CSI-RS rate matching.For example, the terminal may perform rate matching according to theindication of the PQI field if the signaling bit is set to 0, andperform rate matching according to the DCI field if the signaling bit isset to 1.

In DCI transmission option 2 for the aperiodic ZP CSI-RS configuration,the indication field shown in Table 8 or 9 is transmitted instead of theexisting PQI field positions. As described above, the terminal usingonly the aperiodic CSI-RS according to trigger option 1 or 2 may be notable to perform the CoMP operation. Hence, instead of transmitting thePQI to such a terminal, the DCI overhead can be reduced and the coveragecan be increased by replacing the corresponding bits with the DCIindicating information for aperiodic ZP CSI-RS transmission.

In DCI transmission option 3 for the aperiodic ZP CSI-RS configuration,the existing PQI field or a new DCI indication is received according tothe base station setting. For example, when the base station sets a1-bit configuration, it is possible to determine whether to use the bitas PQI or a setting field for the aperiodic ZP CSI-RS. In other words,if the received 1 bit is set to 0, the terminal may interpret the bit asa PQI field and perform a CoMP operation according to the QCL and PQIfield settings. If the received 1 bit is set to 1, the terminal mayinterpret the bit as a bit for aperiodic ZP CSI-RS configuration andinterpret it as an indication field shown in Table 8 or 9 to performrate matching. This configuration can be delivered via an additionalDCI, and can also be set via RRC. When configured via the DCI, it ispossible to dynamically switch between the aperiodic ZP CSI-RS and thePQI indication. When configured via RRC, such dynamic switching is notpossible, but the DCI coverage can be improved.

FIG. 13 is a flowchart illustrating operations of the terminal accordingto an embodiment of the present invention.

With reference to FIG. 13, at step 1310, the terminal receivesconfiguration information for the aperiodic CSI-RS. Based on thereceived configuration information, the terminal may identify at leastone piece of information regarding the number of ports for eachaperiodic CSI-RS, the number of antennas per dimension N1 and N2, theoversampling factors per dimension O1 and O2, one piece of subframeconfig for transmitting multiple CSI-RSs, multiple pieces of resourceconfig to set the position, the codebook subset restriction, CSIreporting, the CSI-process index, and the transmission power.

Thereafter, at step 1320, the terminal receives feedback configurationinformation based on at least one CSI-RS position. This information mayinclude information regarding the PMI/CQI period and offset, the RIperiod and offset, wideband/subband indication, and the submode.

At step 1340, the terminal receives a plurality of CSI-RSs in onesubframe based on the configuration information, and estimates thechannel between the antennas of the base station and the receptionantennas of the terminal on the basis of the received CSI-RSs.

The terminal generates the feedback information rank, PMI, and CQI usingthe received feedback configuration at step 1340 on the basis of theestimated channel and a virtual channel added between the aperiodicCSI-RSs.

Thereafter, at step 1350, the terminal transmits the feedbackinformation to the base station at a feedback timing determinedaccording to the feedback configuration of the base station, therebycompleting the channel feedback generation and reporting process inconsideration of the two-dimensional arrangement.

FIG. 14 is a flowchart illustrating operations of the base stationaccording to an embodiment of the present invention.

With reference to FIG. 14, at step 1410, the base station transmits theterminal configuration information on the CSI-RS for channelmeasurement. The configuration information may include at least onepiece of information regarding the number of ports for each aperiodicCSI-RS, the number of antennas per dimension N1 and N2, the oversamplingfactors per dimension O1 and O2, one piece of subframe config fortransmitting multiple CSI-RSs, multiple pieces of resource config to setthe position, the codebook subset restriction, CSI reporting, theCSI-process index, and the transmission power.

Thereafter, at step 1420, the base station transmits the terminalfeedback configuration information based on at least one aperiodicCSI-RS. This information may include information regarding the PMI/CQIperiod and offset, the RI period and offset, wideband/subbandindication, and the submode. Then, the base station transmits theconfigured CSI-RS to the terminal. The terminal estimates the channelfor each antenna port and estimates an additional channel for a virtualresource based on the channel estimation result. The terminal determinesthe feedback, generates the corresponding PMI, RI, and CQI, andtransmits the generated information to the base station.

At step 1430, the base station receives feedback information from theterminal at a given timing, and may utilize the feedback information toexamine the state of the channel between the terminal and the basestation.

FIG. 15 is a block diagram of a terminal according to an embodiment ofthe present invention.

With reference to FIG. 15, the terminal includes a communication unit1510 and a controller 1520. The communication unit 1510 transmits orreceives data to or from the outside (e.g., base station). Here, thecommunication unit 1510 can transmit feedback information to the basestation under the control of the controller 1520. The controller 1520controls the states and operations of all the components constitutingthe terminal. Specifically, the controller 1520 generates feedbackinformation according to information allocated from the base station.The controller 1520 controls the communication unit 1510 to feedback thegenerated channel information to the base station according to thetiming information allocated from the base station. To this end, thecontroller 1520 may include a channel estimator 1530. The channelestimator 1530 determines required feedback information based on theCSI-RS and feedback allocation information received from the basestation, and estimates the channel using the received CSI-RS based onthe feedback information. The channel estimator 1530 decodes the PDSCHbased on the PRG size and the rank corresponding to the PDSCHtransmission described in embodiments of the present invention and byapplying the reference signal mapping to the DMRS port with an appliedprecoder on the basis of the DCI received from the base station. In FIG.15, the terminal is depicted as having the communication unit 1510 andthe controller 1520. However, without being limited thereto, theterminal may further include various components according to theirfunctions in the terminal. For example, the terminal may further includea display to display the current state of the terminal, an input unit toreceive an input signal from the user for function execution, and astorage to store data generated in the terminal. Although the channelestimator 1530 is depicted as being included in the controller 1520 inthe above description, the present invention is not limited thereto. Thecontroller 1520 may control the communication unit 1510 to receiveconfiguration information for each of reference signal resources fromthe base station. The controller 1520 may also control the communicationunit 1510 to measure the at least one reference signal and to receivefeedback configuration information from the base station so as togenerate feedback information according to the measurement results.

The controller 1520 may measure at least one reference signal receivedthrough the communication unit 1510 and generate feedback informationaccording to the feedback configuration information. The controller 1520may control the communication unit 1510 to transmit the generatedfeedback information to the base station at the feedback timingdetermined according to the feedback configuration information. Thecontroller 1520 may receive the CSI-RS (channel statusindication-reference signal) from the base station, generate feedbackinformation based on the received CSI-RS, and transmit the generatedfeedback information to the base station. Here, the controller 1520 mayselect a precoding matrix for each antenna port group of the basestation, and may select an additional precoding matrix based on therelationship between the antenna port groups of the base station.

The controller 1520 may receive the CSI-RS from the base station,generate feedback information based on the received CSI-RS, and transmitthe generated feedback information to the base station. Here, thecontroller 1520 may select one precoding matrix for all antenna portgroups of the base station. The controller 1520 may receive feedbackconfiguration information from the base station, receive the CSI-RS fromthe base station, generate feedback information based on the receivedfeedback configuration information and the received CSI-RS, and transmitthe generated feedback information to the base station. Here, thecontroller 1520 may receive feedback configuration corresponding to eachantenna port group of the base station and additional feedbackconfiguration based on the relationship between the antenna port groupsof the base station.

FIG. 16 is a block diagram of a base station according to an embodimentof the present invention.

With reference to FIG. 16, the base station includes a controller 1610and a communication unit 1620. The controller 1610 controls states andoperations of all the components constituting the base station.Specifically, the controller 1610 allocates CSI-RS resources for channelestimation to the terminal and allocates feedback resources and feedbacktimings to the terminal. To this end, the controller 1610 may include aresource allocator 1630. The controller 1610 allocates feedbackconfigurations and feedback timings so that feedbacks from pluralterminals do not collide, and receives feedback information at the settiming to analyze the feedback information. The communication unit 1620transmits or receives data, reference signals, and feedback informationto or from the terminal. Here, the communication unit 1620 transmits theaperiodic CSI-RS to the terminal through the allocated resources, andreceives the feedback on the channel information from the terminal underthe control of the controller 1610. In the above description, theresource allocator 1630 is included in the controller 1610, but thepresent invention is not limited thereto. The controller 1610 maycontrol the communication unit 1620 to transmit configurationinformation for each of at least one reference signal to the terminal,or may generate the at least one reference signal. The controller 1610may control the communication unit 1620 to transmit feedbackconfiguration information to the terminal so as to generate feedbackinformation according to measurement results. The controller 1610 maycontrol the communication unit 1620 to transmit the at least onereference signal to the terminal and to receive feedback informationfrom the terminal at a feedback timing determined according to thefeedback configuration information. The controller 1610 may transmitfeedback configuration information to the terminal, transmit theaperiodic CSI-RS to the terminal, and receive feedback informationgenerated based on the feedback configuration information and the CSI-RSfrom the terminal. Here, the controller 1610 may transmit feedbackconfiguration information corresponding to each antenna port group ofthe base station and additional feedback configuration information basedon the relationship between the antenna port groups. The controller 1610may transmit the terminal the CSI-RS beamformed based on the feedbackinformation, and may receive feedback information generated based on theCSI-RS from the terminal. According to the embodiments of the presentinvention described above, it is possible to prevent the base stationthat has a large number of transmit antennas with two-dimensional arraystructures from allocating excessive feedback resources for CSI-RStransmission. It is also possible to prevent an increase in channelestimation complexity of the terminal. The terminal can measure all thechannels for a large number of transmit antennas, compose feedbackinformation based on the measurement results, and report the feedbackinformation to the base station in an effective manner.

Hereinabove, embodiments of the present invention have been describedwith reference to the accompanying drawings. Specific terms or wordsused in the description should be construed in accordance with thespirit of the present invention without limiting the subject matterthereof. It should be understood that many variations and modificationsof the basic inventive concept described herein will still fall withinthe spirit and scope of the present invention as defined in the appendedclaims and their equivalents.

What is claimed is:
 1. A method performed by a terminal in a mobilecommunication system, the method comprising: receiving, from a basestation, information on a type of a plurality of channel stateinformation-reference signal (CSI-RS) resources, the type of theplurality of the CSI-RS resources including an aperiodic type and asemi-persistent type; receiving, from the base station, a medium accesscontrol (MAC) control element (CE) indicating at least one of theplurality of the CSI-RS resources; and receiving, from the base station,a CSI-RS based on the CSI-RS resources indicated by the MAC CE.
 2. Themethod of claim 1, wherein, in case the type of the plurality of theCSI-RS corresponds to the aperiodic type, the method further comprising:receiving, from the base station, downlink control information (DCI)indicating at least one of the CSI-RS resources indicated by the MAC CE;and receiving, from the base station, the CSI-RS on the CSI-RS resourcesindicated by the DCI.
 3. The method of claim 1, wherein, in case thetype of the plurality of the CSI-RS corresponds to the semi-persistenttype, the method further comprising: receiving, from the base station,the CSI-RS periodically on the CSI-RS resources indicated by the MAC CE.4. The method of claim 1, further comprising: receiving, from the basestation, information associated with a quasi co-location (QCL)relationship between a demodulation reference signal (DMRS) for aphysical downlink shared channel (PDSCH) and the CSI-RS; and receiving,from the base station, the PDSCH based on the information associatedwith the QCL relationship, wherein the DMRS of the PDSCH is quasico-located with the CSI-RS with respect to Doppler shift, Dopplerspread, average delay and delay spread.
 5. A method performed by a basestation in a mobile communication system, the method comprising:transmitting, to a terminal, information on a type of a plurality ofchannel state information-reference signal (CSI-RS) resources, the typeof the plurality of the CSI-RS resources including an aperiodic type anda semi-persistent type; transmitting, to the terminal, a medium accesscontrol (MAC) control element (CE) indicating at least one of theplurality of the CSI-RS resources; and transmitting, to the terminal, aCSI-RS based on the CSI-RS resources indicated by the MAC CE.
 6. Themethod of claim 5, wherein, in case the type of the plurality of theCSI-RS corresponds to the aperiodic type, the method further comprising:transmitting, to the terminal, downlink control information (DCI)indicating at least one of the CSI-RS resources indicated by the MAC CE;and transmitting, to the terminal, the CSI-RS on the CSI-RS resourcesindicated by the DCI.
 7. The method of claim 5, wherein, in case thetype of the plurality of the CSI-RS corresponds to the semi-persistenttype, the method further comprising: transmitting, to the terminal, theCSI-RS periodically on the CSI-RS resources indicated by the MAC CE. 8.The method of claim 5, further comprising: transmitting, to theterminal, information associated with a quasi co-location (QCL)relationship between a demodulation reference signal (DMRS) for aphysical downlink shared channel (PDSCH) and the CSI-RS; andtransmitting, to the terminal, the PDSCH based on the informationassociated with the QCL relationship, wherein the DMRS of the PDSCH isquasi co-located with the CSI-RS with respect to Doppler shift, Dopplerspread, average delay and delay spread.
 9. A terminal in a mobilecommunication system, comprising: a transceiver configured to transmitand receive a signal; and a controller associated with the transceiverand configured to: receive, from a base station, information on a typeof a plurality of channel state information-reference signal (CSI-RS)resources, the type of the plurality of the CSI-RS resources includingan aperiodic type and a semi-persistent type, receive, from the basestation, a medium access control (MAC) control element (CE) indicatingat least one of the plurality of the CSI-RS resources, and receive, fromthe base station, a CSI-RS based on the CSI-RS resources indicated bythe MAC CE.
 10. The terminal of claim 9, wherein, in case the type ofthe plurality of the CSI-RS corresponds to the aperiodic type, thecontroller is further configured to: receive, from the base station,downlink control information (DCI) indicating at least one of the CSI-RSresources indicated by the MAC CE, and receive, from the base station,the CSI-RS on the CSI-RS resources indicated by the DCI.
 11. Theterminal of claim 9, wherein, in case the type of the plurality of theCSI-RS corresponds to the semi-persistent type, the controller isfurther configured to: receive, from the base station, the CSI-RSperiodically on the CSI-RS resources indicated by the MAC CE.
 12. Theterminal of claim 9, wherein the controller is further configured to:receive, from the base station, information associated with a quasico-location (QCL) relationship between a demodulation reference signal(DMRS) for a physical downlink shared channel (PDSCH) and the CSI-RS,and receive, from the base station, the PDSCH based on the informationassociated with the QCL relationship, wherein the DMRS of the PDSCH isquasi co-located with the CSI-RS with respect to Doppler shift, Dopplerspread, average delay and delay spread.
 13. A base station in a mobilecommunication system, comprising: a transceiver configured to transmitand receive a signal; and a controller associated with the transceiverand configured to: transmit, to a terminal, information on a type of aplurality of channel state information-reference signal (CSI-RS)resources, the type of the plurality of the CSI-RS resources includingan aperiodic type and a semi-persistent type, transmit, to the terminal,a medium access control (MAC) control element (CE) indicating at leastone of the plurality of the CSI-RS resources, and transmit, to theterminal, a CSI-RS based on the CSI-RS resources indicated by the MACCE.
 14. The base station of claim 13, wherein, in case the type of theplurality of the CSI-RS corresponds to the aperiodic type, thecontroller is further configured to: transmit, to the terminal, downlinkcontrol information (DCI) indicating at least one of the CSI-RSresources indicated by the MAC CE, and transmit, to the terminal, theCSI-RS on the CSI-RS resources indicated by the DCI.
 15. The basestation of claim 13, wherein, in case the type of the plurality of theCSI-RS corresponds to the semi-persistent type, the controller isfurther configured to: transmit, to the terminal, the CSI-RSperiodically on the CSI-RS resources indicated by the MAC CE.
 16. Thebase station of claim 13, wherein the controller is further configuredto: transmit, to the terminal, information associated with a quasico-location (QCL) relationship between a demodulation reference signal(DMRS) for a physical downlink shared channel (PDSCH) and the CSI-RS,and transmit, to the terminal, the PDSCH based on the informationassociated with the QCL relationship, wherein the DMRS of the PDSCH isquasi co-located with the CSI-RS with respect to Doppler shift, Dopplerspread, average delay and delay spread.